Where can I get a depth micrometer and how to test with it?

[joshdaskew]

Hi, I have recently got into large format photography and have a Chamonix 45N-1. I went through a whole bunch of grief with the groundglass/fresnel lens issue associated with this camera, as I was shooting with a Xenotar 150mm 2.8 and was consistently getting stationery subjects coming back out of focus. I thought i was going mad to be honest until I slowly but surely saw other people appearing on this forum with similar issues.

This issue has since been resolved by having a Maxwell screen installed and my back being measured by Bill Moretz at ProCamera. So far so good with the results..

In my quest for information with regards to shooting wide open with this lens, he said that as depth of field was so minimal at that aperture, that I would also need a darkslide that was in very close relation to the groundglass back..

Since then, I have read a few articles that state what the ANSI standards are for darkslides ( 0.197 +or- 0.007 ) and that ultimately film holders depth should be aiming for 0.190. For example, apparently Sinar manufactures its backs to 0.190.

This is one article that I am referring to

http://www.largeformatphotography.in...-holders.3.gif

So my first question is, if the standard is + or - 0.007 why is the depth we are aiming for 0.197. Isn't that only taking into account the minus. Wouldn't it be a range from 0.190 to 0.204?

Most articles seem to aim for this number of 0.190, could someone please explain this to me?

Also, recently I had a friend test some of my darkslides at a printing factory where he works and I was surprised at what some of them came back as. Most were pretty good but one came back as 0.224! Just on one side as well..

So, I was hoping that someone could suggest an online store or something where I could buy a depth micrometer that wasn't super expensive and was capable enough of testing my double dark slides.

I live in Melbourne, Australia and have enquired at a few stores without much success ( not that were reasonably priced anyway ).

I did see this one on Ebay but am not even sure if this is what I am after...

http://cgi.ebay.com/200-mm-Digital-C...#ht_2119wt_941

It also states that it is accurate to 0.02mm or 0.001in, is this enough?




Any information that any one could provide would be greatly appreciated! Best Regards Josh

Oh yeah, and if anyone could please pass on a good test with such an instrument that would be awesome.. Thanks again.

[D. Bryant]

Hi, I have recently got into large format photography and have a Chamonix 45N-1. I went through a whole bunch of grief with the groundglass/fresnel lens issue associated with this camera, as I was shooting with a Xenotar 150mm 2.8 and was consistently getting stationery subjects coming back out of focus. I thought i was going mad to be honest until I slowly but surely saw other people appearing on this forum with similar issues.

This issue has since been resolved by having a Maxwell screen installed and my back being measured by Bill Moretz at ProCamera. So far so good with the results..

In my quest for information with regards to shooting wide open with this lens, he said that as depth of field was so minimal at that aperture, that I would also need a darkslide that was in very close relation to the groundglass back..

Since then, I have read a few articles that state what the ANSI standards are for darkslides ( 0.197 +or- 0.007 ) and that ultimately film holders depth should be aiming for 0.190. For example, apparently Sinar manufactures its backs to 0.190.

This is one article that I am referring to

http://www.largeformatphotography.in...-holders.3.gif

So my first question is, if the standard is + or - 0.007 why is the depth we are aiming for 0.197. Isn't that only taking into account the minus. Wouldn't it be a range from 0.190 to 0.204?

Most articles seem to aim for this number of 0.190, could someone please explain this to me?

Also, recently I had a friend test some of my darkslides at a printing factory where he works and I was surprised at what some of them came back as. Most were pretty good but one came back as 0.224! Just on one side as well..

So, I was hoping that someone could suggest an online store or something where I could buy a depth micrometer that wasn't super expensive and was capable enough of testing my double dark slides.

I live in Melbourne, Australia and have enquired at a few stores without much success ( not that were reasonably priced anyway ).

I did see this one on Ebay but am not even sure if this is what I am after...

http://cgi.ebay.com/200-mm-Digital-C...#ht_2119wt_941

It also states that it is accurate to 0.02mm or 0.001in, is this enough?




Any information that any one could provide would be greatly appreciated! Best Regards Josh

Oh yeah, and if anyone could please pass on a good test with such an instrument that would be awesome.. Thanks again.

The tool with the ebay link will work just fine. I would think if you live in a large metro area these tools would be easy to locate.

I've forgotten why 0.190 is the standard depth now so perhaps someone else will chime in.

Don Bryant

[jp]

The image refers to a machinist's micrometer, which could very well be something like this: (and I have no affiliation or recommendation for this particular seller)

http://cgi.ebay.com/Vintage-Metric-D...item3effa753ba

Search for depth micrometer. The flat part would sit flush on the film holder and you'd spin the dial to lower the plunger rod into the film holder. Where it hit your film would be the depth. You could also remove your ground glass back and measure the distance between the face of the back and the ground glass in the same manner.

[mrossano]

Using a dial or digital caliper to take depth measurements on groundglass frames or film holders is neither convenient nor likely to produce an accurate measurement. Use a dial depth gage, such as this tool:
http://cgi.ebay.com/Fowler-Dial-Dept...item3ca88ac00a
which is a reverse reading dial indicator with a depth gage base. The correct nominal depths for 4x5 are 4.80mm for the groundglass and 5.00mm for the film holder (0.189" and 0.197", respectively). This provides an allowance of 0.008" for the film (0.007" film thickness + 0.001" air gap behind the film). ANSI tolerances are pretty loose. You should try to hold your equipment dimensions to +/- 0.002".

[RichardRitter]

The 0.197 is the distance from the face of the holder to the septum of the holder. Film is 0.004 to 0.008 thick depends on the make of film. The film also sits in a slot that is 0.012 min. So the film can float around in that slot. Most camera makers take the "T" dim and subtract the thickness of the film for the distance of the focusing plane of the ground glass.

In your case I would adhere the film to the holder if you want to use the lens wide open less chance of the film not being in the same focusing plane as the ground glass. Given all the pluses and minus can add up to the film being 0.025 off from where you focused the camera.

[Scott Walker]

I have no idea about the standard measurement but I can tell you a bit about the tool in question.

Your link shows a Vernier Caliper and more specifically a digital version of the tool. These calipers are available in the standard version, a dial version and the digital version. They also come in a stamped steel form, a molded plastic form, and a machined steel form, I am sure I don't have to explain which is the most accurate.

To use this type of caliper to measure depth you need to use a straight edge across the piece you want to measure, the measurement is made with the small rod that extends out of the tail or ruler looking part of the tool. This tool is not really the best tool for this type of measurement but if you do not need accuracy better than 1 or 2 thousandths of an inch it is more than adequate.
One thing I would recommend for someone that does not use one of these tools on a regular basis is to buy the digital version or maybe the dial version, my employees all were taught to use the dial version and for some it was a pretty hard learning curve at first.

Idealy you would use a depth micrometer but they are expensive and are dififcult to use if you are not familiar with micrometers.


One last thing, the more money you spend the more accurate your measurements will be, that is just a simple rule when it comes to measuring tools.

[Ivan J. Eberle]

Basically you want to confirm that your film holder is right in the ballpark and not the major factor in unsharp image.

While you don't need to have the perfect production tool, a simple caliper, either digital or vernier, is a poor choice. A depth guage is a rather specialized tool; it seems to me you'd need to make a jig out of plate with bores plate to do much film holder or GG testing, anywhere but at the edges. Besides, you're not setting up to build them, you just want to confirm that the holders you've got don't suck.

For this, a dial indicator and a stand on a surfacing block should work as rapidly and as well as anything (short of a production testing jig for a depth gauge), and they're very common and versatile tools. Inexpensive ones can be found at places like Harbor Frieght Tools. Any Sears tool department of any size should carry one. Anyone you may know who is an automotive mechanic or a machinist will probably have several and may even lend you one and a stand.

Dial indicators have moving plungers and a round dial with a watch-hand scale that's easy to read (unlike a depth gauge's vernier scale). .001" accuracy is close enough for this work but get one with at least a quarter of an inch of measuring range, and a straight plunger not a lever-type will be easiest to set up. For what you're doing a smooth formica counter-top should be an adequate substitute for a granite surfacing block.

Once you've got the dial indicator set up in a stand perpendicular to the surface, lower the plunger onto the pressure plate/film well/septum until there's some slight tension from spring pressure, then lock down your adjustable stand. The tool is then zeroed by rotating the rim of the dial. Hopefully you will have set it up with .197" or more of travel, if not it'll soon be obvious and simple enough to adjust. The film holder is laid on it's back and slid around under the indicator to see the variation or warp. Measuring the step up/down to the frame will reveal the depth (it's okay to assist the plunger up on the 90˚ step up but you don't want to disturb the heavy base, just gently retract the plunger). The difference in the reading is your depth. Simpler to do than describe, once you have the tools in hand.

I've been a mechanic and a hobby machinist for so long that eyeballing .003 to .005" out of true is pretty routine, but also find a straight-edge is handy for speedily confirming that a holder is warped.

[Jeffrey Sipress]

0.1968" equals 5 millimeters. That's where it comes from.

I know exactly what you are talking about, but I'm sure you don't actually mean to use the term 'darkslide' when it reality the dimension in discussion is to the ground side of your glass.

[Glenn Thoreson]

Depth of field is extrememely shallow with your lens wide open (millimeters). If you look closely, you should see one quite small detail in your print that is sharp. That will give you an idea of just how shallow it is. I check questionable film holders with a sheet of film in place. Measure the depth from the face of the film to the face of the holder. Measure the ground side of the glass to the face of the focus panel. They should agree within a few thousandths of an inch. If you go to the auto parts store you should be able to buy something that will work to measure it. It's not that critical. I find the depth gauge on my best digital calipes and a sraightedge works just fine. I still think you have a depth of field issue more than anything.

[Drew Wiley]

The tail of a digital caliper can be used for measuring depth, but a digital depth micrometer per se would be best for this. Any machinist's supply has them, as well as
ordinary industrial outlets like Grainger. Mitutoyo and Starrett are especially good brands. What I did to precisely measure the film plane and camera back alignment is to take a bar of precision ground Starrett flat stock, which is extemely flat and straight, drill a hole in the center, and mount the depth micrometer there. This allowed
me to discover any discrepancies in the film plane due to bubbles in paint or varnish
or whatever and correct them to within a thousanth of an inch. Overkill no doubt,
since film in a filmholder is seldom that flat, but every little bit helps.