phase contrast q's

Have questions about the equipment used for macro- or micro- photography? Post those questions in this forum.

Moderators: rjlittlefield, ChrisR, Chris S., Pau

GaryB
Posts: 521
Joined: Fri Jul 29, 2016 12:18 pm

phase contrast q's

Post by GaryB »

How much of a difference is there between a budget phase objective and a good one, given the limitations in effective na and color restrictions inherent in phase? I bought a cheap used Beck 40/.65 phase and it looks ok, but as it's the only phase objective I've ever owned I have no way of knowing what I might be missing. In brightfield it's pretty mediocre, my poorest performing 40x by quite a margin in fact if that's any indication.

G

zzffnn
Posts: 1896
Joined: Thu May 22, 2014 1:25 pm
Location: Houston, Texas, USA
Contact:

Post by zzffnn »

Gary,

To my eyes, there is a visible difference between Apo (phase) objective and achromat (phase) objective of similar NA. Apos produce cleaner images and resolve slightly better. But depending on cost difference, that image quality difference may or may not be worth it.

Personally, when I am on budget, I always pay for features that I want (such as water immersion) first and foremost, then I put my money on NA value (I usually like higher NA for my water protists). Apo or not is usually my last concern. But then in my particular case, the only water immersion objectives I can easily buy happen to be LOMO high NA apos (with two exceptions); so I happily bought them.

Best way to decide if the difference is worth it for you is to image the same exact subject, at same exact focus plane, using achromat phase objective and apo phase objective of about the same NA. Then compare results. Sorry, I cannot help now as I am moving and my scope has been packed.

I agree that some phase objectives do not perform very well in brightfield. My LOMO apo phase 70x NA 1.23 water objective did not perform as well as its plain brightfield version (the phase version produced a brownish color tint under oblique light, while BF version was a bit cleaner). But I kept the phase 70x and sold the BF 70x, because I prefer its water phase feature and already have a good water apo 65x NA 1.1 BF.

Beck objectives are said to be very good in general though, when compared within the same class (achromat vs achromat).

I have asked an expert for you, hopefully he will comment in this thread.
Selling my Canon FD 200mm F/2.8 lens

GaryB
Posts: 521
Joined: Fri Jul 29, 2016 12:18 pm

Post by GaryB »

Thanks, fan.

I still need a 20x first, then I'll venture into a better 40x.

phil m
Posts: 162
Joined: Sun Aug 10, 2014 2:45 pm

Post by phil m »

I assume that the "Beck" objective is an English RJ Beck objective , not a Conrad Beck and Sons ( CBS) objective? CBS, may be 170mm( anyone on the forum , know for sure?) , whereas Beck is 160mm. Is it being used in a Beck phase stand, with a Beck condenser?
If it is a 160mm objective in a 160mm stand, then it also really needs to be installed in a system that is critically matched to it. ...proper phase ring in a proper condenser. Rarely, does a particular brand phase objective work in another brand's system, although sometimes some adjustments can be made or even a phase ring of another magnification be used, with success.

The fact that the objective is outperformed by other 40X objectives in BF is not surprising. The ring causes the slowdown of a significant portion of the rays putting them out of phase and in BF this shows up , in my experience as a loss of contrast and resolution, irregardless of brand. Phase objectives are usable for BF in a pinch or as a quick check during use of a phase stand but the loss in quality is not acceptable generally.

There is no doubt that phase objectives manufactured to fluorite or apochromat corrections provide superior performance, when used in the correct phase system. Some very transparent or difficult to image small organisms or details are often visible, when only barely or not at all with achromat systems and the objectionable halo, that so plagues some achromat systems is not so apparent, resulting in details showing up better, especially when peripheral to the structure; cilia , the flagella base, difficult to image epiphytes, cell walls and cell unions, chromosomes, lots of stuff.

However, some of those objectives can be really expensive and when compared to the possibilities inherent with various other techniques, other phase formats, anoptral,bright,B-Minus L, variable contrast levels, DF, COL, Rheinberg etc., some of which are fairly easy DIY conversions, depending on cost and the needed results, that expense might be over the top. There were not too many made for 160mm systems, they are more often than not specific to a system and usually the objectives are expensive. Lomo are an option, they are often inexpensive but it would be experimental to determine compatibility or the possibility of DIY'ing a compatible condenser adaption.

zzffnn
Posts: 1896
Joined: Thu May 22, 2014 1:25 pm
Location: Houston, Texas, USA
Contact:

Post by zzffnn »

Gary,

Phil M is the expert that I referred to.

Personally, for my water protists, I think an 100x phase objective would be more useful than a 20x phase.

At 20x objective magnification and NA, your oblique and darkfield should would so well that you would rarely need phase. Suitable subjects for 20x typically have good enough contrast too, such that phase may not be necessary. I would still recommend getting a 20x phase objective, but I recommend getting a 100x phase objective first.
Selling my Canon FD 200mm F/2.8 lens

GaryB
Posts: 521
Joined: Fri Jul 29, 2016 12:18 pm

Post by GaryB »

Phil, fan, thanks for the info

It is indeed a CBS Beck. It's listed as 160/0.17 so it's the right length. I get the feeling it's only a problem when used as brightfield. With phase, I get great contrast, good resolution and overall I'm very happy with the results, I was just curious about whether there might be more I'm missing, having nothing to compare it to.

As for condensers, I've tried numerous options and the best overall is a 40mm LED ring about 45mm below the condenser. I've tried an annulus over the lamp, in the condenser filter holder, direct LED with annulus and direct LED ring, both without condenser. All work pretty well and I have almost infinite control of position and annulus size. I love experimenting :roll: The ring light through the condenser seems optimal for contrast and lesser halo effects. I checked the light to annulus size and it's an ideal match, just a tad inside the objective phase ring boundaries with no spill.

One option I'm looking at as a replacement later is the Zeiss Neofluor 40x .75 as they are reasonably priced and will suit my microscope better. My current setups are a Zeiss standard and Lomo Biolam.

Ichthyophthirius
Posts: 1152
Joined: Thu Mar 07, 2013 5:24 am

Post by Ichthyophthirius »

I can highly recommend the Zeiss Neofluar 40/0.75 Ph2. Excellent, crisp contrast (though it is not a Plan objective).

This is a video of Paramecium that gives a good impression https://www.youtube.com/watch?v=MLs3yeNo8AE

GaryB
Posts: 521
Joined: Fri Jul 29, 2016 12:18 pm

Post by GaryB »

Thanks, Ichthy.

The Neofluar 16 Ph2 looks good too.

ChrisR
Site Admin
Posts: 8668
Joined: Sat Mar 14, 2009 3:58 am
Location: Near London, UK

Post by ChrisR »

I see very few low magnification, eg 4x phase objectives. I assume that's becase there aren't so many larger objects which are hards to see with BF. Is that all there is to it?
Chris R

GaryB
Posts: 521
Joined: Fri Jul 29, 2016 12:18 pm

Post by GaryB »

I would assume so. I can't think of that many things to use phase with below 10x but I'm sure there are cases.

JohnyM
Posts: 463
Joined: Tue Dec 24, 2013 7:02 am

Post by JohnyM »

ChrisR wrote:I see very few low magnification, eg 4x phase objectives. I assume that's becase there aren't so many larger objects which are hards to see with BF. Is that all there is to it?
They are often found on inverted microscopes for petri dish scanning. I personally cant see any other application for this kind of lens, as there is always a better solution with other kinds of subject.

@GaryB can we see a photo with problematic lens? You would be hard pressed to see a difference between phase and ordinary lens with most cases. Most obvious difference are "donuts" in out of focus area, somehow similar to those of mirror lenses.

GaryB
Posts: 521
Joined: Fri Jul 29, 2016 12:18 pm

Post by GaryB »

It's main problems are really poor chromatic aberrations and low contrast. It just looks bad compared to my other achromats. In phase mode it looks as good as many videos I see on youtube.

Ichthyophthirius
Posts: 1152
Joined: Thu Mar 07, 2013 5:24 am

Post by Ichthyophthirius »

GaryB wrote:It's main problems are really poor chromatic aberrations and low contrast. It just looks bad compared to my other achromats.
That's normal for a phase contrast objective used in brightfield, especially for the 40:1. I find it very noticible. It's less of a problem with the 16:1 or 25:1.

GaryB
Posts: 521
Joined: Fri Jul 29, 2016 12:18 pm

Post by GaryB »

hat's normal for a phase contrast objective used in brightfield, especially for the 40:1. I find it very noticible.
Ah, good to know. That's what made me wonder if it was simply a poor lens and whether it was causing problems while using it in phase mode, but it looks fine and you'd have no idea it was so bad in brightfield. I didn't try it in brightfield until a few days after getting it because I already have a par focal Wild fluotar 40/0.75 to use for that, as well as a Lomo, a Leica, a Leitz and a Zeiss. My small collection of 40's is getting silly, yet I will undoubtedly get more :D

JohnyM
Posts: 463
Joined: Tue Dec 24, 2013 7:02 am

Post by JohnyM »

Im tempted to do shots with phase vs normal objective, and check if you can see the difference. In the meantime, Charles Krebs already did similar comparision, tho without pixel level and not brightfield:
http://www.photomacrography.net/forum/v ... php?t=6647

Post Reply Previous topicNext topic