Focus accuracy issue with Intrepid 8x10

[Sam L]

Thank you all for the helpful ideas. I tried adding temporary shims between the camera body and the spring back to push the ground glass away from the lens. With about 0.09" of shim, the image on the ground glass matches the test photo. This is a big shim and makes me doubt my testing, though the preponderance of evidence does suggest I have a real issue.

The distances are very small and it's hard to be confident, but I'm an amateur machinist and happy to take some measurements.

The film holder I ran the newspaper test with is a Lisco Regal II (modern plastic, not wood). I do notice a bit of a rise in the edge just under where the logo is, but it's flexible there and it gets pushed flat by the rear standard when in the camera (otherwise it would leak light). I measured T for the film holder at the 4 corners where it's easy to measure using my old browne and sharpe depth gauge and gut checked the measurements with my modern mitutoyo digital vernier calipers. The corners measure 0.2670" and 0.2675" at the bottom. At the top where the rim bows up I get 0.2750", 0.2740". I believe these are all a little high but within the spec for an 8x10 film holder. I don't have an appropriate flat bar to check the center, but a 150mm machinist rule placed across the span of the septum does not show any light through peeking underneath. It is flat enough for my purposes and I think the film holder is not the issue. Anecdotally, I saw the same focus issue across all 8 of my film holders, which are various brands of modern plastic holders.



Next, I pulled off the revolving back and measured the "T" at the left and right sides of the ground glass where it's easy: 0.211", 0.214".



0.2600" (spec) - 0.2125 (average measured) = 0.0475". With the film holder's T being a little high, this accounts for about half of the focus problem.

The rest of the issue is a bit speculative. It could be user error or lack of precision in my test. However, I notice is that there's always a 1.25mm gap at the top of the spring back because the springs aren't strong enough to get a good mating surface:



There is no gap at the bottom and even slight pressure closes the gap, e.g. from using a loupe against the glass. The gap doesn't explain the front-focusing problem because the gap would act like a shim and improve the issue. But, I also notice that when I apply enough pressure to close the gap, the top of the rear standard flexes towards the lens. it appears that the aluminum base of the camera between the tripod mount and the rear standard is not very rigid.



Thinking through this requires some mental gymnastics, but I think it may explain the rest of the problem. If I push the rear standard towards the lens with my loupe, the focal point will move towards infinity. If I then focus on my subject while applying that same pressure, I will move the lens further away from the ground glass to compensate. When I release the pressure from the loupe, the image will be front focused but I won't know. This is a guess but could explain a 1mm to 2mm focusing error and could be worse if the focusing point is at the top of the glass, which flexes the most.

I think I will try adding 0.05" of shim under the ground glass and run the test again. I also reached out to Intrepid but they probably won't get back to me until after the weekend.

[knjkrock]

Is this why Mr Ritter offers a film plane calibration service?

[Sam L]

I added 0.05" and the focus improved a bit but not enough. Left is before shimming, right is after.



In the ground glass, I focused on the word "the" in the phrase "celebrating the arrival." You can see the focus shifted from the beginning to the end of the word "celebrating" but not far enough. This lends weight to my temporary shimming experiment, which suggested I needed 0.9".

I wonder what intrepid will say. With this much shimming, the screws that hold the retaining springs for the glass will have to be replaced. I guess this stuff doesn't matter for landscapes at f/22...

[Sam L]

Knjkrock,

Could be, because this is really time consuming and tedious. My thinking is one of:

- My camera has a defective rear standard (manufacturing defect)
- They are using the same rear standard for cameras with and without a fresnel sandwich. A fresnel in front of the ground glass might take up 0.1"
- You get what you pay for. These cameras cost around 10% of nice name-brand ones.

[Tin Can]

You are learning many things

Keep at it, the springs must push/hold the holder snuggly

I have a NOS Detective camera for Police work, it had 2 leaf springs both sides, KODAK made in Britain

Very tightly held the DDS, too much, so I removed a leaf from each side

Now perfect

[Bernice Loui]

Back up to the original image goal of full lens aperture (f6.8 in this example) 8x10 portrait, focused on the eye then allowing the remainder of the portrait sitter's face to gradually go out of focus.

This style of 8x10 portrait has been around for a very, very very long time. Few appreciated the demands placed on the camera, film holder, film flatness and more to achieve the intended image goals.

Compounding what happened, low cost, low precision-accuracy, low stability-rigidity, lightweight field folder view camera being put into a very demanding image making need.

Possible defective camera, yet there will be more than a few that would have never revealed this problem in their 8x10 image making or un-aware of this problem until this camera got pressed into trying to meet these requirements-demands. Think f64 ideology-mind set, this camera might be ok with the lens stopped down to f64 making landscape images. That user could be absolutely happy with this camera as it has produced the expected results..


If one were to examine the overall system and what happened, could go like this:

~Idea to make 8x10 portraits could be great.
~Don't want to spend too much $ for a long list of reasons.
~Web driven fashion directs to this as being the low $ answer to what is most desirable in a 8x10 and popular view camera on the market today.
~Camera, lens, film holders, film and related is procured.
~Fueled by the newness and excitement of making the idea of this style of 8x10 portraits happen is strong.
~Much effort and resources get put into the image goal... only to discover the results did not meet the idealized image goal...
~Disappointment and related emotions set in.
~Find help..

Post to LFF notes this could be a ground glass to film in film holder dimension problem.
~Image maker has enough knowledge and measuring tools needed to assess this problem with some guidance from LFF and previous LFF post on this specific problem.
~Measurements made, specifications noted and compared to reveal there is a problem with this camera.
~Problem found passed in to the camera manufacture. Their reply will be very telling in many ways.


Point of this being, and example of image goals, lens then camera and all related to follow. The image goal was to create 8x10 portraits with large aperture lenses. This requirement puts very specific demands and requirements on the camera to support this requirement. Many who have never done 8x10 view camera images like this might have no idea or realization of the precision-accuracy required to achieve the image goals of large lens aperture portraits (as noted by shimming by 0.05" did not properly correct the ground glass to film in film holder dimension problem). These dimension numbers do provide some idea and reality of what is required to achieve absolute registration between ground glass image to film in film holder tolerances involved.


As for this camera being "10%" of nice name brand" cameras, not true. The Intrepid 8x10 list for 480 GBP or $637 USD.
https://intrepidcamera.co.uk/product...id-8x10-camera

As of now there are two monorail 8x10 cameras with lenses for not much more:

8x10 Arca Swiss with 300mm convertible Symmar, $800 USD.
https://www.seawood.shop/acra-swiss-...00-500-f5.html

8x10 Sinar P with 10" Kodak Commercial Ektar, $1600 USD.
https://www.seawood.shop/sinar-8x10-...lens-good.html

For comparison, this is one of four ground glass to film in film holder locating pegs on a 5x7_13x18cm Sinar P2 film holder back. The entire assembly is made of cast aluminum then precision machined, calibrated to meet the industry specification for film in film holder specifications. These parts being made of cast aluminum will be stable, rigid and very durable.





And yes, there are plenty of GOOD wood cameras that meet this same requirement for precision-accuracy-stability. Think Century studio portrait camera (9A and ..) and many others.

More web shopping and waiting for a good deal often results in a better, nicer camera with none of these problem. The camera might need a proper service and fixing. Once done, that camera will be good for many years ahead. Both of these 8x10 view cameras are perceived as FAR less desirable due to them being ~monorail~ view cameras. Yet they are precisely the kind of camera that offers and has designed and built in the accuracy-precision-stability required to achieve the initial image goals. As for the extra $, consider the time, resources and more spent trying to deal with all that has happened so far.

Does what happened impact motivation and interest to continue on with the LF view camera journey?



Bernice

Could be, because this is really time consuming and tedious. My thinking is one of:

- My camera has a defective rear standard (manufacturing defect)
- They are using the same rear standard for cameras with and without a fresnel sandwich. A fresnel in front of the ground glass might take up 0.1"
- You get what you pay for. These cameras cost around 10% of nice name-brand ones.

[Sam L]

Hi Bernice!

I would say that is pretty accurate, though I bought the camera for less (about $500 USD new). The price has gone up a bit, the GBP was weak, etc. It seemed like a great deal at the time and it would sell at a profit on ebay right now so maybe it was.

I shoot 95% landscape on medium format and 4x5, so this very light and compact camera is ok for that kind work (as you say). However, the amount of shimming the ground glass needs to be in spec is a disappointment. I didn't expect precision, but 0.05" is a fat shim.

I have since figured out that I don't want to tote around an 8x10 camera for landscape work and I don't enjoy the attention that it draws when I take it outside. My friend and I have been practicing studio lighting and I thought it would be fun to use the big camera with the lights. I was indeed surprised by how much precision this style of photography demands. I guess I had taken for granted the inherent precision and rigidity of the technical 4x5 that I normally use. Focus changes in the millimeter range can easily ruin the image and this camera just doesn't have that kind of precision. The rear focus screw and linear rails are really good but it isn't rigid and the tolerances aren't tight. Even locked down, the rear standard has some play and the camera base allows for significant flex. The rear fiberglass springs don't hold the glass against the rear standard when there's no film holder in it. The gap is only a few millimeters, but that is the difference between focusing on the eye and the eyebrow.

If I decide to pursue 8x10 studio work, I will likely get a more appropriate camera for it.

As to your question about motivation to continue with large format photography, I don't think that's an issue. Everything I've experienced with learning large format is like this and every used camera I have ever (dozens) had needed some work. One big difference here is that this is a new camera -- the only new film camera I've ever bought, so it is disappointing.

[Sam L]

In other news, I have achieved good focus (on the vertical line).



To get this, I:

1. Shimmed the ground glass to match the "T" of the film holder. For my camera this was 0.05" / 1.25mm. These are so fat that it required shimming the small springs that clamp the glass down as well.
2. Clamped the top of the ground glass holder to the rear standard while focusing. The clamp closed the 1.5mm gap at the top while not putting any pressure on the rear standard causing it to flex forward. I will also have to ask Intrepid about the springs.



3. Screwed down all four of the rear standard nuts extra tight.

Even with these fixes, I found the focus moved around a bit between shots. I'm not totally sure where the movement is coming from but I suspect the rear standard slips a little when the film holder is inserted and/or removed. The movement is so small I can't see it on the camera, only as a slight focus change.

I'm not confident the camera can do this consistently but I believe the ground glass is now calibrated correctly.

[Bernice Loui]

Suggestion, if you continue with this LF view camera journey highly suggest getting a GOOD Sinar Norma or some variant of the Sinar system.
What is needed, a modular view camera system that can be made up as needed for your image goals in mind.

Personally, this would be absolutely intolerable behavior from any view camera.

Studio lighting can be LOTs of fun. For portraits "hot" lights can work GOOD. If strobe is used not too much power is needed even for 8x10 given this style of large aperture portraits. For table top with diffusion and other light modifiers, figure no less than 4000 watt/seconds of strobe power with more than one flash head. Larger the object to be images, strobe power demands goes up real fast. If color film is involved, strobes must have consistent color temperature (5000K +/- less than 100-300K) and consistent flash power adjustable to 0.1 f-stop and not vary per flash cycle.

Know as your experience, image making needs continue to develop and grow, they will greatly increase the demands placed on camera, lenses and every part-aspect of your view camera outfit. Even tiny bothersome things that were once easily tolerated become no tolerance at all once very specific expectations, demands and more are placed on every aspect of the view camera image making system.

No customer should need to "shim" any new view camera to get the ground glass to film in film holder dimension proper. IMO, this is a fundamental and basic view camera functionality. Again, most telling is how the manufacture responds to this problem.


Bernice

Hi Bernice!

I would say that is pretty accurate, though I bought the camera for less (about $500 USD new). The price has gone up a bit, the GBP was weak, etc. It seemed like a great deal at the time and it would sell at a profit on ebay right now so maybe it was.

I shoot 95% landscape on medium format and 4x5, so this very light and compact camera is ok for that kind work (as you say). However, the amount of shimming the ground glass needs to be in spec is a disappointment. I didn't expect precision, but 0.05" is a fat shim.

I have since figured out that I don't want to tote around an 8x10 camera for landscape work and I don't enjoy the attention that it draws when I take it outside. My friend and I have been practicing studio lighting and I thought it would be fun to use the big camera with the lights. I was indeed surprised by how much precision this style of photography demands. I guess I had taken for granted the inherent precision and rigidity of the technical 4x5 that I normally use. Focus changes in the millimeter range can easily ruin the image and this camera just doesn't have that kind of precision. The rear focus screw and linear rails are really good but it isn't rigid and the tolerances aren't tight. Even locked down, the rear standard has some play and the camera base allows for significant flex. The rear fiberglass springs don't hold the glass against the rear standard when there's no film holder in it. The gap is only a few millimeters, but that is the difference between focusing on the eye and the eyebrow.

If I decide to pursue 8x10 studio work, I will likely get a more appropriate camera for it.

As to your question about motivation to continue with large format photography, I don't think that's an issue. Everything I've experienced with learning large format is like this and every used camera I have ever (dozens) had needed some work. One big difference here is that this is a new camera -- the only new film camera I've ever bought, so it is disappointing.

[Graham Patterson]

Interesting, but scary. I have access to an original Kickstarter model of the 8x10. Measuring from the camera-side face of the frame to the GG surface in several places with a digital caliper I found:

0.227 in measured = 5.766mm

ANSI 8x10 holder
0.260 in = 6.604mm
+/- 0.016 in = 0.406mm

Discrepancy 0.033 in = 0.838mm or about twice the ANSI allowance.

In this case the ground glass needs to be moved away from the lens, either by sanding down the GG reference points (ouch!), or by adding material to the face of the GG frame, which would be simpler. Simplest of all would be a replacement GG frame to standard.

At least with this camera the ground glass frame seems mate evenly with the camera back.