Bright vs Dark Phase Contrast

[rnabholz]

I was recently lucky enough to add some new tools to the kit, a set of Bright Phase Contrast objectives.

American Optical Spencer Bright Phase Contrast objectives

BPO Lineup BP.JPG (158.11 KiB) Viewed 12058 times

So I made a trial run to compare the images from the Bright vs Dark. I did my best to match focus by choosing a single feature and attempting my best focus on it. Exposure was the same for each, only resizing, minor level adjustments and light unsharp mask was applied.

I welcome all of your thoughts regarding what you see.

Bright

Phase 3777.JPG (102.9 KiB) Viewed 12058 times

Dark

Phase 3779.JPG (91.39 KiB) Viewed 12058 times

Bright

Phase 3776.JPG (132.49 KiB) Viewed 12058 times

Dark

Phase 3775.JPG (122.29 KiB) Viewed 12058 times

[rnabholz]

More

Bright

Phase 3788.JPG (88.8 KiB) Viewed 12057 times

Dark

Phase 3789.JPG (74.65 KiB) Viewed 12057 times

Bright

Phase 3797.JPG (96.19 KiB) Viewed 12057 times

Dark

Phase 3801.JPG (85.04 KiB) Viewed 12057 times

[rnabholz]

more

Bright

Phase 3770.JPG (86.05 KiB) Viewed 12056 times

Dark

Phase 3771.JPG (67.86 KiB) Viewed 12056 times

Thanks for looking.

Rod

[zzffnn]

Bright phase sees deeper, which was why I mostly bought bright phase and not dark phase.

Rod,

All those were imaged with 100x phase, correct?

Wwould you please show 45x dark phase vs 45x bright phase vs 100x dark phase vs 100x bright phase, in terms of background color and contrast (please try to pick a similar central area for all 4 objectives)?

My dry bright phase looked quite light in background color, while oil bright phase looked like yours (if not slightly darker). I am guessing difference was caused by oil immersion vs air and itheir optical interaction with mountant (Pleurax).

I just bought a 97x B-Minus and now have both B-Minus and bright phase in 43x and 97x / 95x. I may have an extra oil bright phase 97x or 95x for sale soon. All are 160TL, 34 mm parfocal AO Spencer.

[75RR]

Great first image!
Bright Phase working a bit better in this comparison.
I do think that it might be unfair to use the same light setting on both.
Might that be hamstringing the Dark Phase a little?

[rnabholz]

zz - I will do more experimentation later and post the results here

75 - Thanks. Your point about the exposure is a good one. There is certainly an opportunity to increase the exposure a bit to dig out some more detail in the background. The habit of basing the exposure on aesthetic considerations for a selected subject probably doesn't serve well in this comparison exercise.

Thanks

Rod

[KurtM]

Good luck adjusting the exposure - the trouble I always run into with dark phase is the dynamic range challenge is as bad or worse than dark field. That is, if you properly expose the bright areas, the darker areas get underexposed; conversely, if you adjust for the darker regions, then the bright parts get blown out. Looking at your dark phase images here, I don't see where you can brighten up the darks very much without blowing out the brights. Well I gotta take that back to some degree: you can accomplish a lot in post processing. But light levels are much more evenly balanced in bright phase, and dynamic range simply not a problem.

In my opinion, bright phase delivers more information on prepared diatom mounts than dark phase. But dark phase does show some details better. So while the best is having both, given a choice of only one, make mine bright phase, please.

Lovely images!

[75RR]

I tried fiddling with the Dark Phase in Photoshop to no good effect - think you got the most out of it.

I hope you do not mind if I re-post 2 of the images (untouched, just reduced canvas size) side by side for a better comparison.

[zzffnn]

I don't know exactly how, but you should be able to compress dynamic range with curve adjustment. That should help the dark phase.

Basically, increase exposure for under exposed, decrease those over's, and keep the middling the same. Contrast adjustment with curve can do similar things.

Shooting RAW will give you more range of adjustment too. Shooting jpeg provides very limited adjustment range.

[charlie g]

Hi all, thanks Rod for this informative shoot-out on your phase objectives.

For me the lighter background images all manifest a crisper focus regards to those diatom frustule 'dots', vrs the dark back ground images. So I will not say the dark phase objective is a weaker performer based on these images.

My 1985 Nikon Labophot Phase brochure up front states:


"A high transmission green intyerference filter is provided for maximum contrast." I have this filter yet have never used it for the years my circa 1980's Nikon Labophot has been my workhorse stand. My former workhorse stand still proudly sits in a backburnercorner of my cluttered study..hats off to you nobel circa 1960's Austriaa/Reichert Biozet!

Nikon terms their phase (1980's speak that is) : DL, DM, and BM...they list a series of each and specimens these best perform with..it's a concise page of a 1985 brochure I have.

I love the 20X Plan-achro BM, and the DL series of objectives for my live protist microscopy.

Perhaps we all should try a green filter with our phase contrast? thanks again, Rod! charlie guevara

[rnabholz]

Good luck adjusting the exposure - the trouble I always run into with dark phase is the dynamic range challenge is as bad or worse than dark field. That is, if you properly expose the bright areas, the darker areas get underexposed; conversely, if you adjust for the darker regions, then the bright parts get blown out. Looking at your dark phase images here, I don't see where you can brighten up the darks very much without blowing out the brights. Well I gotta take that back to some degree: you can accomplish a lot in post processing. But light levels are much more evenly balanced in bright phase, and dynamic range simply not a problem.

In my opinion, bright phase delivers more information on prepared diatom mounts than dark phase. But dark phase does show some details better. So while the best is having both, given a choice of only one, make mine bright phase, please.

Lovely images!

Good point about the dynamic range limitation, as you and zz say, curves can help some, but can also reduce contrast which can work against our purpose of digging out detail.

For analysis purposes bright does seem to have an advantage, but I have to say aesthetically, I do prefer dark.

Thanks

[rnabholz]

I tried fiddling with the Dark Phase in Photoshop to no good effect - think you got the most out of it.

I hope you do not mind if I re-post 2 of the images (untouched, just reduced canvas size) side by side for a better comparison.

Always feel free to grab and massage any of my images, just be prepared to teach me what you did!

Thanks for the effort and interest.

Rod

[zzffnn]

Perhaps we all should try a green filter with our phase contrast?

Charlie G,

My eyes vastly prefers green filtration for achromat phase contrast on subjects without color. But I usually prefer "scientific clinical" in a boring way (I am rarely artistic).

As I understand, Rod prefers to keep colors in his phase images, for aesthetic/artistic reasons.

To each his own.

[rnabholz]

Thanks Charlie,

I am no stranger to the positive benefits of green filters, as I use then regularly in my darkfield shooting. I have not done so yet with phase, but your post reminds me to try it sooner than later.

Thank you

Rod

[KurtM]

For analysis purposes bright does seem to have an advantage, but I have to say aesthetically, I do prefer dark.

I agree: dark phase is much more pleasant to take in visually, as a general thing.

[rnabholz]

Back with more comparison shots.

Below are shots comparing the Bright Phase 45x to Dark Phase 40x in Natural, Green Filtered and Green Filtered converted to Grayscale. Also the same sets of the Bright and Dark 100x,

The same focus point was selected for both series, and was in the left most Cocconeis form. I did change the focus point between the 40x and 100x series as the difference in magnification and depth of focus made it difficult to maintain the same point. Exposure was lengthened for the green filtered shots as the same exposure as unfiltered was underexposed. I have grouped the shots below in pairs of matching types.

Dark Phase 40x.JPG (103.79 KiB) Viewed 11969 times

Bright Phase 45x.JPG (96.17 KiB) Viewed 11969 times

Dark Phase 40x Green.JPG (82.77 KiB) Viewed 11969 times

Bright Phase 45x Green.JPG (81.56 KiB) Viewed 11969 times

[rnabholz]

Continuing...

Dark Phase 40x Gray.JPG (70.91 KiB) Viewed 11968 times

Bright Phase 45x Gray.JPG (71.12 KiB) Viewed 11968 times

Now 100x

Dark Phase 100x.JPG (77.95 KiB) Viewed 11968 times

Bright Phase 100x.JPG (85.35 KiB) Viewed 11968 times

[rnabholz]

More...

Dark Phase 100x Green.JPG (68.07 KiB) Viewed 11968 times

Bright Phase 100x Green.JPG (75.32 KiB) Viewed 11968 times

Dark Phase 100x Gray.JPG (58.81 KiB) Viewed 11968 times

Bright Phase 100x Gray.JPG (64.72 KiB) Viewed 11968 times

[zzffnn]

Very nice and helpful, thank you Rod.

Is your bright 40x and bright 100x of the same contrast level? Say, both are L or M? Did you visually see a lighter background in 40x image, than camera's capture?

The background difference between my 43x Bright M phase and 95x bright phase seems much more, with the 43x Bright M being much lighter. My 95x Bright is a vintage one that does not say contrast level. Edit: maybe it is just my particular slide and/or my eyes (I did not photograph them).

I prefer converted green images, but that is just my peculiar eyes.

[rnabholz]

I can't say that I have had enough time with them to have any firm impressions or draw any hard conclusions.

I do think the photos above do pretty accurately represent what I was seeing visually.

I don't think these objectives have any other designation other than "bright".

Rod

[apochronaut]

Your dark phase are plan? If so, they were a somewhat improved objective over the dark and bright phase achromats, which were based on the 1076,1077,1078 and 1079, series of lenses. AO seemed content to relegate bright phase to the also ran file, and never made a set of bright plans.
The default contrast level for the infinity corrected bright, dark and plan dark was M and for the lone B-Minus objective, it was L.

[charlie g]

Thanks for this extended shoot-out,Rod. For me you get a sense of being underwater with the green filtration..I begin to hear those odd sounds I pick up when I swim under water..the green converted to grays seems best to my eyes.

Regards to dynamic range issues with all these phase images...for me it's almost as if these objectives function best for live and moving targets visually..rather than image captures..the bright haloes and bright structures all are accomodated by my visual system, vrs digital image captures.

I feel like I'm enjoying a glossy graphic novel with your dark phase images..I enjoy this sense!

thanks, charlie guevara

[rnabholz]

Your dark phase are plan? If so, they were a somewhat improved objective over the dark and bright phase achromats, which were based on the 1076,1077,1078 and 1079, series of lenses. AO seemed content to relegate bright phase to the also ran file, and never made a set of bright plans.
The default contrast level for the infinity corrected bright, dark and plan dark was M and for the lone B-Minus objective, it was L.

Yes the Dark Phase are Plan.

Thanks for the info on contrast levels.

Rod

[rnabholz]

Thanks for this extended shoot-out,Rod. For me you get a sense of being underwater with the green filtration..I begin to hear those odd sounds I pick up when I swim under water..the green converted to grays seems best to my eyes.

Regards to dynamic range issues with all these phase images...for me it's almost as if these objectives function best for live and moving targets visually..rather than image captures..the bright haloes and bright structures all are accomodated by my visual system, vrs digital image captures.

I feel like I'm enjoying a glossy graphic novel with your dark phase images..I enjoy this sense!

thanks, charlie guevara

Thanks Charlie

I agree on the green, it is too much for me too. Fortunately the conversion to a more comfortable gray is easy and preserves the advantage of the green filtration.

Glad you find the thread interesting and worth while. Thanks for your interest and comments.

Rod

[apochronaut]

I'm not sure the use of the green filter was ever designed with colour photography in mind. It's a tool for black and white, which until the mid 80's or so was the dominant choice in film.....in some cases the only practical choice, due to ease of processing and cost.

[rnabholz]

I'm not sure the use of the green filter was ever designed with colour photography in mind. It's a tool for black and white, which until the mid 80's or so was the dominant choice in film.....in some cases the only practical choice, due to ease of processing and cost.

A very good point. I guess we quickly forget those days.

I dipped plenty of Tri-X and Panatomic-X, in Microdol-X or D76. I could certainly see labs doing their own developing, both for convenience and control.

Now I click a mouse. Can't say I don't like it a lot better these days.....

Thanks APO.

Rod