9 replies to this topic

[LTrimmer331]

Hey all! 

 

I recently discovered the world of trichrome photography and I keep coming back to the idea of trichromatic film astrophotography. I know that monochrome CCD users will image using RGB filters and I wondered if the same sort of process was possible with film. I found some dichroic color filters (Rosco Permacolor, designed for lighting) that are relatively inexpensive that I want to play with and am going to give it some good old trial and error experimentation! 

 

 

As for the forum post: I need some advice 

 

      Most of my experience is digital. I have attempted film photography maybe twice with varying levels of success, so my experience is quite limited. 

 

What film stocks would you recommend I use for this process? (35mm) 

What is the easiest way you have found to focus your camera?

What sort of issues could I potentially run into with this process (including tracking) and how can I mitigate them? 

What targets would be a good place to start given the time of year? (Northern hemisphere) 

Should I consider a light pollution filter as well as the RGB? (I generally observe in Bortle 4 with a large light dome to the north) 

How long of exposures would you recommend I start with? (I do understand reciprocity failure) 

 

 

 

Lots of questions, I know. Thanks for your time! 

 

 

My equipment: 

Camera: Canon FTB QL 

Lens: Canon FD 300mm f/2.8 L + optional 2x teleconverter

Mount: Sky Watcher Star Adventurer 2i (not autoguided, but I am considering it) 

 

[Michal1]

Why do you think that the tricolor approach would give you better results than color film? Yes, in the past monochrome films were faster, but today? Really, I don't know, you would have to try. In any case, I would recommend you to first learn astrophotography with color film and go the harder way after.

 

Rick Thurmond, who has not been active in this forums for some time, did tricolor astrophotography. Look for his posts. Here is his web page: http://www.rickthurmond.com/ I remember that he was using Fuji Acros 100 and Kodak Techpan.

 

The exposure times will depend on the film you use. With Acros 100, it would be like 1h at f/4.

 

You will use a relatively short lens, whose focus should not depend much on temperature. So I would recommend that you find the exact infinity position on the focusing ring using daytime objects or the Moon. You will draw a mark on your lens and use it at night.

 

Targets for a 300mm lens for spring? Not many. Try to catch some objects in the winter Milky Way in the evening. Or later in the spring, there will be the Galactic center rising toward the morning. You can also take photos of galaxies, that the spring sky is full of, but be prepared that they will be very small in the photos.

[Todd N]

Green and especially blue color filters don't work well with B&W film for astrophotography. They are inefficient compared to yellow through red filters which will have a peak transmission of 90% or more and pass all the spectrum above their spectral cut off. Blue and green are around 50 to 60% and bracket the spectrum further limiting the overall light hitting the film.  In the last couple of years, I tried Fuji Acros which has excellent performance with a blue filter and got next to nothing. Back in the day, tri-color with Techpan was done but that film had superior performance once hypersensitized. The general rule was to double the exposures for the blue and green filters compared to the red. Some of these color composite images could be over three to five hours of imaging time. Use color film as the previous poster suggested. 

[Michal1]

And I recalled another page with tricolor images:

http://astrophotogra...org/index1.html

[LTrimmer331]

Thanks for the feedback!

 

I looked into the photos by Rick Thurmond and he's got some great results, although given my limitations I fear I won't be able to recreate his process as well as he did

 

I may still give it a shot just to satisfy my curiosity, but what I'm hearing that it may be a much bigger hassle than it's worth.

 

Thanks again! 

[TxStars]

What is the main reason you want to try tricolor ?

 

Tricolor film work basically died when Kodak quit making Techpan

Through some testing you might be able to find a B&W film for the Blue and the Green.

You will likely have to use a color film for the Red.

 

Techpan does come up for sale from time to time, but there is no guarantee it will still be good.

 

 

 

Attached Files

•  Techpan2415.pdf   166.78KB   3 downloads

[LTrimmer331]

What is the main reason you want to try tricolor ?

I think it is a curiosity about the process more so than anything else. I got into film photography and processing a while ago and it's just been something that keeps popping in my mind to try

 

 

I was reading about Tech Pan and hyper-sensitization being the main reason for it's popularity. Do you know of any other films that are good with reciprocity either with or without being hypered? 

[xonefs]

I think it is a curiosity about the process more so than anything else. I got into film photography and processing a while ago and it's just been something that keeps popping in my mind to try

 

 

I was reading about Tech Pan and hyper-sensitization being the main reason for it's popularity. Do you know of any other films that are good with reciprocity either with or without being hypered? 

 

It has been said already but Fuji Acros II is the best current BW film but it is not very sensitive to Ha which wouldn't make it great for mono tri band imaging. Tech pan was unique in that it was responsive through the deep red. There are no current BW films like that which also react well to hypering or have decent reciprocity. 

[Horologium1959]

Offhand, I think I will throw this out there in case anyone might find it useful. 

In the 1970s Astronomy Magazine did a how article on tri-color astrophotography.

Some of the films mentioned are certainly discontinued, but the article might still be useful to 

anyone who wishes to pursue this.

I do not remember if the article mentioned any film still in production like Tri-X.

 

Hope this helps!

[TxStars]

To just learn the process of tricolor grab some color film.

Print film has more dynamic range so it would be a good choice.

Kodak Ektar 100 / Gold 100 or 200 / Portra 400 would be good choices.

Shoot one exposure with each filter then scan & combine them in software.

 

* You can also bracket exposures for each filter and use masking to create a higher dynamic range image

 

** Do not use a LPR filter as that will shift everything to the red.

Edited by TxStars, 16 March 2023 - 01:56 PM.