Beam Splitting vs Switching Trinoc and Image Brightness

[rnabholz]

My AO Series 4 trinoc head is the switching type, throw a lever to direct 100% of the light to either the eyepieces or to the camera.

I recently came across another version, one using a beam splitter to "share" the light and allow for visual and photography to occur simultaneously. I thought it might be a nice feature to have so I picked it up.

I finally got around to giving it a try last weekend, and it really surprised me. My pre-buy concern is that the beam splitter would mean that the views at the eyepiece and the light reaching the camera would both be reduced, and would affect the visual brightness and lead to increased exposure time on the camera. It seems that neither is the case. The views are bright, and I find that I have to speed up the shutter to get a good exposure versus the settings I used on the other trinoc.

I am pleased, but stumped. So what is it I don't understand about the way these things work?

[PeteM]

Rob, our eyes pretty easily adapt to various levels of illumination. So, it's not surprising that there isn't an easily seen difference in the eyepieces when some percent of the light (50%?) is diverted to the camera. Only when you have a direct comparison, such as with a three-position beam splitter is it easy to notice the reduced light from sharing those photons.

What IS surprising is that you seem to be getting more light to the camera. Seems to me there are just two possibilities. One is that your existing 100-100 head has significant losses (poor coatings or other optical faults). The other that you may not really have an apples to apples comparison in exposure times with all other things being equal. Among the possible differences might be a different image size captured with the old and new trinocular heads?

[rnabholz]

Hi Pete,

Thanks for your thoughtful response.

As you say, discerning a slight difference in brightness visually with out having scopes set up side by side is probably not realistic, and that was not that part that had me perplexed.

You correctly homed in on the real head-scratcher part, why the increased light to the camera?

I have not done extensive experimentation and trials managing all of the potential variables, (and probably won't ;^) ). I can say that I have had this scope for a while now, have shot thousands of images through it, nearly all of which are diatoms, most of which were brightfield or oblique, and a pretty good feel for the exposures. I am seeing a 2 to 4 stop difference.

As to the possible issues you raised, I believe the image scale is comparable. It very well may be that the 100/100 head is a bit dingy inside - it is after all approaching around 60+ years old, and I have only had custody for the last couple, so who knows what it has been through.

You seem to confirm that my original confusion is founded in some semblance of reason - a welcome change for me, so I thank you for that. ;^)

Rod

[MicroBob]

Hi Rod,
to narrow the possibilities down - can you see how the light path in your 100/100 tube is? Is there a polarizer or ND filter in there?
I would expect that in the modern tube at least 50% of the light would be directed to the photographic branch, but not 200 to 400%

Bob

P.s.: I just got an attractive business idea - lets continue this via pm!

[rnabholz]

I will take a look, I'm not sure.

[apochronaut]

Knowing these heads quite well and having them both, I am pretty sure that your 0/100 head has light loss somewhere. When I have a minute , I will test the versions I have here, which are both very clean. 60 year old heads can have a considerable layer of very fine airborne debris. Remember , they come from an era when people smoked at dinner,in bathrooms, airplanes, while making dinner, vacuuming the closet, in changerooms, showers,at confession and even while fixing gas leaks on cars.

[rnabholz]

Knowing these heads quite well and having them both, I am pretty sure that your 0/100 head has light loss somewhere. When I have a minute , I will test the versions I have here, which are both very clean. 60 year old heads can have a considerable layer of very fine airborne debris. Remember , they come from an era when people smoked at dinner,in bathrooms, airplanes, while making dinner, vacuuming the closet, in changerooms, showers,at confession and even while fixing gas leaks on cars.

I think you are on the money with the light loss from uncleanliness theory. I would be interested to see how the two compare when operating properly.

I will say that using the beam splitter version is more convenient.

Any optical quality differences between the two that should be considered?

Thanks Apo

Rod

[KurtM]

...an era when people smoked at dinner,in bathrooms, airplanes, while making dinner, vacuuming the closet, in changerooms, showers,at confession and even while fixing gas leaks on cars.

And he ain't stretching the truth either! Every time I look back on those days I just can't believe it really was like that!

[MicroBob]

I have to do with smoke detectors. Once I got one in my hands that was medium brown from cigarrette smoke after just 6 months. I don't this that is was ready to action in this period - activated it would have been on alarm all the time. Incredible what human beeings can survive!

I can imagine that a 100/100 trino head is slightly superior in photo quality as there is no need for much glass in the photo branch.