Focal plane light meters

[DogsAfire]

I am shooting 4x5 using a Zeiss Ultraphot microscope (see http://farm7.staticflickr.com/6014/5932441596_8f62c3e17b_b.jpg). Typical scene metering with a hand-held is simply out of the question, since the "scene" exists only within the instrument. Metering is especially problematic for darkfield, which is akin to determining the exposure for a bright sparkling jewel sitting on a completely black background. I need a light meter that works at (on the film side of) the ground glass. It is a job that really requires a spot meter. I don't want to work from the back side of the glass, if that's even an option, because I have multiple focus screens that have different fresnels for optimal viewing brightness under different conditions.

It appears that the Sinar Six and Sinar Booster will do the job, but they don't seem to be available anymore. They are not even mentioned on Sinar's site. Are there other companies who provide this type of meter? What is the best way to approach this issue?

Thanks

[ic-racer]

The Horseman focal plane light meter was made for many years in various configurations of 6x9 and 4x5. Early ones are more difficult to use because of the need for innovative battery solution, but they cost less.

[vinny]

watch ebay. the meters come up on occasion.
I'm from cross village. Where bouts are you?

[Nathan Potter]

Nice setup you show there. I'd be inclined to use a good DSLR attached to one of the oculars using a conventional microscope adapter. Use the reading on the DSLR (area or spot) to obtain an exposure reading then work out the correction factor for a 4X5 film through trial and error.

Nate Potter, Austin TX.

[ic-racer]

Have you considered the Gossen microscope adapter?
85670

[lenser]

Gossen also made (makes?) a fiber optic probe with a reading cross section of only a couple of millimeters. The one that I have will work on my Luna Pro with some math gymnastics, but it's actually designed to work on the Lunasix.

Minolta made an accessory kit for their flash meters called the Booster II which can also do continuous light readings. There are several different items in the kit, one of which is a very precise probe. I believe this plugs into pretty much all of their digital meters. I use mine with my Minolta Flash III and it can do exactly as you describe your needs. I found mine on ebay a few years ago.

Both read directly from the back of the ground glass for extremely precise measurements of a very limited target area.

[cowanw]

The Horseman meter is an averaging meter not a spot meter. it works well. The battery issue doesn't seem to be a problem. But I don't see it working for Darkfield except by experience.

[ic-racer]

The 6x9cm Horseman meter is quite 'center weighted' on 4x5" format. A simple mask can turn it in to a spot meter of just about any proportion. Also, do you not have any assortment of objectives for a high magnification spot reading?

[DogsAfire]

Wow! Thanks for the replies everyone. More than I expected.

Ic-racer - Thanks for the tip on Horseman. Conanw (below) adds that the Horseman meter is averaging. That could be a problem for the darkfield work. If you happen to know differently, please pop back in here and tell us.

The Microscope adapter that you show appears to slip over an eyepiece tube. Unfortunately, one of the primary configurations that I want to use is what Zeiss calls a "simple microscope". It uses the Luminar lenses (this is the camera that was designed to be a companion to the Luminars - there is even a lever that swings in an additional lens marked "Luminar") and has no eyepieces. A large globular head containing mirrors takes the place of the normal binocular head. So this pretty much eliminates anything that uses an eyepiece or normal phototube.

Vinny - I looked at eBay and actually found two meters, but I'm still a bit unsure just what I am looking at and what the capabilities are. I may simply buy one on the assumption that there's got to be a way I can get a repeatable measurement out of it.
BTW, I'm just down the street from you so to speak. Traverse City. I pop up to Cross Village occasionally for Bliss Fest.

Nathan - As I noted above, there won't be any eyepiece or trinocular tube available. I suppose I could pop off the focus screen to make some sort of measurement. Would you use a lens on the slr or not?

Lenser - I think the probe you are referring to is the one used with the Sinar Six (the Six part of the name comes from the Gossen Lunasix meter that was paired with the probe), but I thought that system was for reading on the face of the glass. The Minolta Booster is definitely for the rear of the glass and it just sounds like a world of headaches to me if there is _any_ other way to accomplish the task. Still, if I can find a reliable spot meter with some sort of "probe on a stick", I think I could probably find a way to make it work.

Conanw - Thanks for the info on the Horseman meter. One of my fantasies for this outfit is to photograph snowflakes in darkfield or Rheinberg illumination (strong, contrasting background colors) and spot readings will be important.

Input from each of you has been helpful and is much appreciated.

Bruce

[lenser]

Dogs,

The Luna six was adapted to the probe you are thinking of which is a stick with a sensor probe that fits under the ground glass. The actual Gossen probe is a flexible fiber optic sheathed in a rubber tube with a direct probe at the end which reads only from the surface of the ground glass while the probe is in contact with the glass at 90 degrees. It reads a target point that is only what you place it directly on.

[Bob Salomon]

There was also the Prontor Magnetic shutter system which also incorporated the spot reading Prontor probe that is the same one that Sinar and Gossen used. The Magnetic System should be real challenging to find though.

[DogsAfire]

Sinar, Gossen and Sekonic have all responded to my inquiries that they no longer make this type of meter

Sinar was kind enough to provide me with an operating manual for the Sinar Six. Is anyone else interested? I looked for a group documents area, but didn't see one. I'll upload the manual if there is a repository of such information for the group.

[cowanw]

If most of your field is black, an averaging meter may be ok. Just close down 3-4 stops from the reading. That's what I meant regarding experience.
I am not thinking you can reasonably mask it to be a spot meter as you cannot see what you are masking. The meter blocks the GG. So you would have to measure things up just so.

[cowanw]

Did you see this
http://www.johndesq.com/pinhole/booster.htm

[Sevo]

Probes can always be found on ebay, and they use a variety of widespread (Gossen Luna Pro, Minolta Flashmeter and Broncolor series) base meters that are just as easy to acquire. Right now, a search for "sinar booster" turns up one complete kit http://www.ebay.de/itm/Minolta-Auto-Meter-IV-mit-Sinar-Booster-1-/370713110511?pt=DE_Elektronik_Computer_Foto_Camcorder_Foto_Camcorderzubeh%C3%B6r_PM&hash=item56503927ef and about ten separate booster probes.

[Nathan Potter]

OK, so you don't have a free ocular for a microscope adapter. Maybe you can meter directly off the GG image plane. At focus there is a real image at the plane and it is visible with the unaided eye when using a frosted screen as is normal in LF photography.

I've not tried this but I suspect you could use a Pentax spot meter with a supplementary lens attached to the front such that the meter to GG distance is reduced to several inches, more or less. A 3 or 4 dioper lens should be adequate.

Now ideally you don't want the GG present but you want to focus on the aerial image that has been placed at the film plane via the microscope focus mechanism. I think the best way to do this would be to employ a partially frosted GG so that the frosted part is used for critical focus with a loupe then the exposure is determined by spot metering the aerial image in the clear part of the glass. Essentially you will be spot metering the magnified image directly and avoiding the variable scattered light directly off the frosted part of the GG. I think such a direct meter reading can be used as read for accurate exposure determination.

Nate Potter, Austin TX.

[DogsAfire]

Cownaw - Thanks for the suggestion and the link. Yes, I had seen the link. Good info there.

Nathan - Yes, metering from the glass is what I had in mind. I have specifically been looking for the meters that read from the front of the glass because I have more than one focus screen. If I read from the back side, I would have to calibrate each glass, possibly at several points across the surface. The original Zeiss focus screens had a big clear X in the middle. Up to now, I had not understood what the purpose of the X was. Now I get it. They allowed a portion of the screen to be clear to allow metering from the back side of the glass. My new screens are from Bill Maxwell and don't have any clear areas.

Sevo - Exactly what I was looking for. Bought it! Thank you. That auction did not show up in my eBay searches.

[Nathan Potter]

Those screens with a clear X are incredibly handy. I just broke my antique one from the 1960s' that came with a Linhof copy setup. Yes you can view the aerial image directly in the clear "X" area from the outside of the focus screen using a loupe. As I mentioned above, I think you can simply use a Pentax spotmeter with a closeup lens for the same purpose plus you get spot metering with good EV accuracy directly. The caveat is you need enough light to obtain a reading.

By the way, I'm not sure Linhof ever made such a screen. Mine had no identifying markings. If you have one, does it have any markings or part numbers?

Nate Potter, Austin TX.

[DogsAfire]

My light meter arrived today! Can't wait to try it out. I also picked up a Polaroid 405 back that will allow me to use the Fuji instant film

Last week I took my first few large format photos with my Ultraphot. Exposure was determined with B/W test shots and a final color test shot.
If you're interested, see http://farm9.staticflickr.com/8497/8334971496_e44926fdc6_b.jpg

Nathan - My focus screens have no identifying marks either. I got my new screens from Bill Maxwell of Maxwell Precision Optics. I assume that Bill is known around these parts. I'm not sure if he could do a clear X or not. You might ask him. The screens are not cheap, but oh my, what a gorgeous image!

[jk0592]

Wow, what a gorgeous image. I am surprised that such a large field is covered by the Ultraphot, the image is reminescent of those that would need a stereomicroscope...

[Nathan Potter]

DogsAfire, that is a beautiful image. If I may ask what is the actual dimension of the wing. Did you use a Zeiss objective in combination with an ocular? These newer Zeiss microscope objectives are among the finest obtainable for resolution and contrast that you can get your hands on. Is your Ultraphot equipped with DIC capability?

I assume that since the FOV is highly planar here you did not employ any focus stacking technique.

Nate Potter, Austin TX.

[DogsAfire]

Thanks for the kind words.

I did do an image stack. I exposed six sheets of film, spaced 20 micrometers apart in depth and covering 100 micrometers (0.1 mm) total depth. As I performed the stacking operation though, it became clear that I could get better results with fewer images. Eventually, I dropped it down to three images in the stack, which is the image that I posted.

I just put up another image which is a single frame from the set of images acquired for the stack. Of the different images that I made, this one has the best overall focus. It is on Flickr at
http://www.flickr.com/photos/31611026@N00/8340922306/

If you can get to the 2048 x 1548 pixel image (click on the image, then look in the upper right for "View all sizes"), you will see all the detail you need. At 2048 x 1548 the image has a magnification of approximately 130x on my screen, but the image should not be viewed that large. It looks much better at half that size, but Flickr appears to compress the image and the 1024 pixel image sufers from the compression.

I apologize for not posting the details of the photograph. I have been writing to the microscopy group as well and I forget what information I posted where. The wing is a bit under 5 mm in length. I used a Zeiss Ultraphot microscope with a 40mm Luminar lens. In this configuration there are no eyepieces and I have to work entirely with the ground glass as an image. The field of view is pretty much maxed out for the 40 mm lens.

As I was typing this I realized that I might have been able to use the 25mm lens (which has a higher numerical aperture) if I also employ the 0.8x reduction lens. I just tested the combination and the wing just barely fits on the 4x5 image area, but it's good enough that it's worth trying another piece of film when I get the chance. An earlier experiment that I did has me thinking that the extra resolution of the 25 mm lens should not be hurt too badly by the 0.8x reduction and that I should get an overall boost in resolution. I'll have to give that combination a try.

Regarding DIC: As its name suggests, the Ultraphot was built to accommodate virtually every offering that Zeiss had available at the time (the Ultraphot was produced from the late 50's through the 70's), so DIC is easily employed - should you have the necessary pieces. Luck came my direction one day a couple years ago when I bought a different microscope. As I unpacked it, I saw a telltale arrow on the condenser. Sure enough, it was a DIC condenser. And a DIC analyzer was right there in the Optovar as well. The seller had not realized that these pieces were special and had simply included them with the scope. Just those two pieces alone could have sold for more than double what I paid for the whole outfit. To date, I haven't used the setup much, but it appears to be functional. I don't believe it would work with the Luminars though, since each DIC prism covers only a certain range of magnifications and the Luminars are very low magnification. I'm not sure how well they would cooperate with the DIC condenser (they have their own specialized condensers).

[Nathan Potter]

Thanks for the detailed info. I was kinda wondering if you might be using Zeiss Luminars. If your subject was about 5 mm in length then your image on a 4X5 GG would be +/- 150 mm so the absolute magnification is around 30X using the 40mm FL Luminar. Not using a compound microscope setup preserves the high quality of the single objective so you're getting a stellar image here. I love those Luminars!

Good deal on accidentally getting part of a DIC setup but you'd need objectives equipped with wollaston prisms to make that arrangement functional. On the other hand I presume you are trans-illuminating the flys wing.

Nate Potter, Austin TX.