Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

How to overcome reciprocity failure on a scope?

  • Please log in to reply
13 replies to this topic

#1 Shakedown St.

Shakedown St.

    Explorer 1

  • -----
  • topic starter
  • Posts: 86
  • Joined: 26 Jun 2017
  • Loc: Boston, MA

Posted 26 June 2018 - 04:10 AM

I am looking to take a few one hour exposures with a film camera I will be attaching to my telescope.

 

For anyone who has shot film with a telescope, how did you personally deal with very long exposures?


Edited by Shakedown St., 26 June 2018 - 04:23 AM.


#2 james7ca

james7ca

    Fly Me to the Moon

  • *****
  • Posts: 5708
  • Joined: 21 May 2011
  • Loc: San Diego, CA

Posted 26 June 2018 - 04:38 AM

I understand that film choices are somewhat limited today. However, some film types suffer less from reciprocity failure and others can be doped or pre-sensitized using a vapor "bath" of certain chemicals. You can also lower the temperature of the film (carefully and during the exposure) and that may also help. However, most of these possibilities are limited today because film is so seldom used for astrophotography (meaning that the required chemicals and/or equipment may be hard to find).

 

Of course, with more-or-less unlimited funds or unlimited amounts of film you could always use a series of short exposures and then digitally scan the many negatives/positives and stack those results as would be done with a digital camera. But that gets pretty expensive and time consuming so I'm not sure how many people have actually tried that approach. In any case, with the levels of light pollution that many of us have it may not be possible to make exposures that last for one or two hours (maybe in the narrow band with filters, but not for full color or even unfiltered, panchromatic black and white unless you image from a relatively dark location).

 

As I am sure you know, film has limits in comparison to what can be done today with digital cameras. However, it's certainly possible to take good images using film, but I'm not certain that it is a good choice for really deep, long-integration-time imaging.



#3 Michal1

Michal1

    Viking 1

  • -----
  • Posts: 549
  • Joined: 25 Jul 2010
  • Loc: Czech Republic, Central Europe

Posted 26 June 2018 - 05:20 AM

There are several ways to reduce the reciprocity failure: film hypering, film cooling, preflashing, pumping dry air inside the camera.

 

In the first place, if you haven't taken any film photo through a telescope, I would recommend to try to make a few shots without these extra complications. I suspect that you will first have to learn to polar align and guide very precisely. It's not easy to make a well guided hour exposure. That's why I created the PARot program for polar alignment. Sometimes, it is better to take 2-3 shorter exposures and stack them digitally.

 

I choose films with a low reciprocity failure.

 

If you elaborate on your experience and possibilities, we might help you better.


Edited by Michal1, 26 June 2018 - 05:34 AM.

  • lee14 likes this

#4 Shakedown St.

Shakedown St.

    Explorer 1

  • -----
  • topic starter
  • Posts: 86
  • Joined: 26 Jun 2017
  • Loc: Boston, MA

Posted 26 June 2018 - 05:43 AM

I started out shooting astrophotography on digital ten years ago. My first scope was a Televue 85 I had attached to my astronomy club's polar aligned mount with a Nikon D5000. I got great shots, but am interested in the resolution possibilities of 6X6 and 8X10 negatives for the night sky.

I have heard you compensate for reciprocity failure by taking longer exposures, and when getting developed in the dark room. I have seen hour long exposures taken on film shown on here, so I do know it is possible somehow. I sometimes do a lot of cropping, I scan my 6X6 negatives at 4000dpi.

#5 TOMDEY

TOMDEY

    Surveyor 1

  • -----
  • Posts: 1582
  • Joined: 10 Feb 2014
  • Loc: Springwater, NY

Posted 26 June 2018 - 06:40 AM

Well, I used to hyper Kodak's TP-2415 "Tech Pan" film using pressurized Hydrogen gas... for a day in an oven. I built all that stuff myself and it Did work magnificently. Then store in the freezer. My scope was 12.5 inch F/6. Exposure times 2 continuous hours for galaxies, 3-5 hours for H-alpha. In the early years, my guide-correction was by hand, pushing buttons. Silicon-based cameras have supplanted all of that. Film would still be fun, but supplies are difficult to find, and expensive!

 

Gas hypering is FAR superior to the other techniques... I've done them all...

 

I'd say Go for It! This is a hobby, after all, and the older techniques are fun to pursue, just for the experience.  Tom

 

Attached Thumbnails

  • 10.0 Supernova.jpg

  • Todd N and coinboy1 like this

#6 Michal1

Michal1

    Viking 1

  • -----
  • Posts: 549
  • Joined: 25 Jul 2010
  • Loc: Czech Republic, Central Europe

Posted 26 June 2018 - 06:44 AM

Not every telescope can cover a 6x6 or 8x10 frame. Many modern telescopes don't cover even a 35mm frame since they are optimized for small digital sensors. What telescope are you going to use? What is its diameter and focal length? How dark is your sky?

 

Yes, it is possible to "push" the film during the development. This push processing increases the detail in the dimmer parts of the image for the price of amplifying the grain. Hard to say if it is advisable. Generally, it is better to increase the exposure time. If you need to keep this time short, for example because of the difficulties with tracking, pushing can be the way to go. One usually determines the exposure time according to own experience or the advice of others with similar equipment and sky quality.

 

People at this forum don't usually do nothing special to reduce the reciprocity failure, me included. Sometimes you can see the pushed images. We just use films with low reciprocity failure. The best films are either the B&W Fuji Acros 100 or Fuji

Provia 100F. Acros has a poor response for red nebulae but it can capture magnificent images of star clouds or dark nebulae. For the red nebulae, use Provia.

 

My advice is to start simply. First see whether you can focus and guide well enough. This is not easy. When you manage that, complicate things further by doing something against the reciprocity failure.



#7 Ian Robinson

Ian Robinson

    Cosmos

  • *****
  • Posts: 9704
  • Joined: 29 Jan 2009
  • Loc: 33S , 151E

Posted 26 June 2018 - 07:37 AM

Hunt down a Lumicon Hypering kit .

Then treat a bunch of rolls of film prior to use and chill it and store in an airtight container .

 

http://siegfriedmani..._17th_nacaa.pdf

The photographic material to be treated is placed in an airtight chamber which is evacuated to approximately ‐70 k p (outgassing) to remove oxygen and water vapour.

 

This is followed by filling the chamber with a non‐combustible forming gas, a mixture of approximately 95% dry nitrogen and 5% hydrogen at pressure of approximately 200kp.

This procedure is repeated to ensure removal of atmospheric gasses.

 

Gas immersion times and temperatures are typically in the region of 6‐48 hours and 20‐50˚C.

 

guide for different emulsions

http://www.csun.edu/...ovin/hyper.html

You can purchase Forming Gas or Hydrogen from many welding supply dealers. Forming gas can be special ordered with various H2 concentrations. An H2 concentration of 8-10% is typical for hypering work.

 

I used to hypersensitise B/W and colour negative (400ASA) 35mm negative film 4 rolls at a time and I'd keep them either in the chamber or place them film in the freezer  prior to use. I still have my kit, but wont be selling it, I plan to use again one day when I get back into imaging.


Edited by Ian Robinson, 26 June 2018 - 07:41 AM.


#8 Todd N

Todd N

    Explorer 1

  • *****
  • Posts: 83
  • Joined: 07 Dec 2007

Posted 30 June 2018 - 05:54 AM

Despite some of the theoretical recommendations here, don't go out of you way trying sophisticated hypering techniques . Most films don't respond to H2 hypering; I've been testing films for several years. I've even tried ammonia and silver nitrate baths that didn't work on whatever film I was testing at the time. You will just be wasting time and money initially going that route.

Preflashing film is simple but needs to be worked out and tested ahead of time.

 

Despite that old principle that slower films have better reciprocity is not the case these days. Aside from the recently defunct Fuji Acros 100, the best off the shelf B&W films are in the ISO 400 range i.g. Kodak Tmax 400, Ilford HP5. Don't waste your time with Tmax 100 or similiar, they're simply not sensitive enough. Likewise high ISO 3200 films are even worse.

 

 

Todd



#9 Achernar

Achernar

    Voyager 1

  • *****
  • Posts: 10853
  • Joined: 25 Feb 2006
  • Loc: Mobile, Alabama, USA

Posted 30 June 2018 - 08:27 AM

There are three ways reciprocity failure were addressed. One is to put the film in an oven and heat it to a specific temperature for a specific duration, after which the film must be exposed and developed immediately. Heat does increase the sensitivity of some films, but it also ages the film faster and increasing fogging. It will not work on all films. Another is to chill it down to the temperature of dry ice during exposure. It works well, but then you have the problem of film becoming brittle as ice at -110F, frosting of the front window of the camera, and the fact you have to load each frame in total darkness in a changing bag. This is a major hassle to do, and again not all films respond well to extreme cold. A third, and the most practical for you is either placing the cassettes or rolls of film in a sealed chamber, then soaking it in a mixture of nitrogen and hydrogen gas. Better results are achieved when the film is places on reels or hangars, then placed in cassettes. The chamber must be light and pressure tight and often is heated to speed the process along. This is the most practical method for amateurs, but you need a gas cylinder and regulator, and a chamber in which to hyper-sensitize your film. This approach works on some films, but either will not work on others, or it will ruin them. It can induce chemical fogging as well, therefore the duration and temperature must be within certain parameters for success. You could use hydrogen alone, but remember this gas is explosive. Nitrogen can be used alone, but its not as effective as hydrogen or a hydrogen/nitrogen mixture called forming gas. It was sold commercially at one time, but now you'd have to find someone who could mix 8 percent hydrogen with 92 percent nitrogen. Once hyper-sensitized, you should use and process the film ASAP. Also, gas hyper-sensitization works by driving oxygen and moisture out of the film, therefore keep it sealed from air exposure and keep it refrigerated or frozen until use. Frankly, I would just opt for a DSLR or CMOS sensor camera and forget about messing with film. I am a former photographer who been down this path, and it's much harder than many realize. You will toss whole rolls of failed exposures into the trash before you get any semi-successful photos.

 

I have some experience with large format cameras too. Yes, the image quality is far superior to 35mm  when it comes to prints of the same size. But few if any amateur telescopes could adequately cover 4 X 5-inch sheet film, let alone 8 X 10 sheet film. Unless you somehow have access to telescopes like the 200-inch Hale telescope in California, I don't know of any amateur instruments that can do that. There are amateur telescopes that can be used with medium format film successfully, but they and a mounting suitable for them are anything but cheap.

 

Taras


Edited by Achernar, 30 June 2018 - 08:38 AM.

  • Uwe Pilz likes this

#10 Michal1

Michal1

    Viking 1

  • -----
  • Posts: 549
  • Joined: 25 Jul 2010
  • Loc: Czech Republic, Central Europe

Posted 30 June 2018 - 11:04 AM

 Frankly, I would just opt for a DSLR or CMOS sensor camera and forget about messing with film.

In my view, film is excellent for bright targets. For capturing dim objects, use a digital sensor -- unless your goal is to do that using film.



#11 Joe F Gafford

Joe F Gafford

    Soyuz

  • ****-
  • Posts: 3545
  • Joined: 15 Dec 2006
  • Loc: Denver, Colorado, US

Posted 30 June 2018 - 03:12 PM

  The best solution was my low F-ratio scopes. My 18" is an F/4.5 scope making the FL of around 2 meters. The same as a C-8 at F/10. Some people were rating film with a C-8. But my fast F-ratio got in the detail of the nebulous objects at the adjusted shorter time then did the C-8 because of the reciprocity feature of the films. A focal reducer did help with the long FL scopes with the high F-ratio, but that increased the field of view and made the object image smaller. 

  Also with hypering, you had to skip the next frame and expose on the following frame or you may have about half of the frame properly hypered as the film loses the hypering as it is exposed outside of the cassette and into the air and humidity. I only hypered once. The results were a little better. However, the next set of emulsions came out with better reciprocity feature and I found that I had a 25 minute limit with my F/4.5 scopes and the F/2.8 Mamiya lens before sky fog came in. 

 

Joe



#12 Joe F Gafford

Joe F Gafford

    Soyuz

  • ****-
  • Posts: 3545
  • Joined: 15 Dec 2006
  • Loc: Denver, Colorado, US

Posted 30 June 2018 - 05:52 PM

Here is an example of hypered older emulsion over a newer one. This was the Kodak Gold series before they tweaked the tabular grain structure of the Royal Gold / PPF Pro films emulsions. This was my only hypered images I've done with the purchased hyper kit with only one fill left in the tank. I done one set earlier with purchased slide film with no comparing with anything. These images were taken 2 months apart with the 2 different emulsion versions of the same brand of film. The hypered top image with filter was a 15 minutes exposure as the lower one was unfiltered and not hypered with a 10 minute exposure. Both images taken hear Kiowa, CO.

 

Hyper_Newfilm_1996.jpg

 

The end strips of both types of film, note the greener cast in the dark regions of the negative with the hypered film?

Hyper_Newfilm_1996_strip2.jpg

 

The rest of the hypered strip. Note the gaps of one frame between exposures. Click to enlarge.

Hyper_Newfilm_1996_strip1.jpg

 

Joe


Edited by Joe F Gafford, 30 June 2018 - 05:54 PM.


#13 SandyHouTex

SandyHouTex

    Soyuz

  • *****
  • Posts: 3539
  • Joined: 02 Jun 2009
  • Loc: Houston, Texas, USA

Posted 01 July 2018 - 06:01 PM

Here is an example of hypered older emulsion over a newer one. This was the Kodak Gold series before they tweaked the tabular grain structure of the Royal Gold / PPF Pro films emulsions. This was my only hypered images I've done with the purchased hyper kit with only one fill left in the tank. I done one set earlier with purchased slide film with no comparing with anything. These images were taken 2 months apart with the 2 different emulsion versions of the same brand of film. The hypered top image with filter was a 15 minutes exposure as the lower one was unfiltered and not hypered with a 10 minute exposure. Both images taken hear Kiowa, CO.

 

attachicon.gif Hyper_Newfilm_1996.jpg

 

The end strips of both types of film, note the greener cast in the dark regions of the negative with the hypered film?

attachicon.gif Hyper_Newfilm_1996_strip2.jpg

 

The rest of the hypered strip. Note the gaps of one frame between exposures. Click to enlarge.

attachicon.gif Hyper_Newfilm_1996_strip1.jpg

 

Joe

Those are some nice pics Joe.

 

Maybe you could consider using dry ice for cooling.  I’m pretty sure there’s some cold cameras in the older Sky and Telescopes if you have them.  It’s the same thing they do to reduce noise in dedicated cmos cameras now.  Heck, you could probably even use some stacked Peltier coolers like the cmos cameras use if you don’t want to use dry ice.  I seem to remember sme outstanding results from them.


Edited by SandyHouTex, 01 July 2018 - 06:02 PM.


#14 Joe F Gafford

Joe F Gafford

    Soyuz

  • ****-
  • Posts: 3545
  • Joined: 15 Dec 2006
  • Loc: Denver, Colorado, US

Posted 03 July 2018 - 09:52 AM

I considered a cold camera setup as the forming gas tank that came with the kit was not legally refillable. The changed reciprocity feature of the newer film within a couple of months back then as the previous post plus my fast F/ratio system catching sky glow more quickly made that a moot point. I don't do film anymore, the enlarger and the rest of the darkroom stuff is stored in my crawl space. My old films are being scanned as needed. I'm getting the footage I shot of the past TSPs I went to in the 1990's cleaned up in Photoshop and will have the first slide show installment starting in 1991 published on YouTube soon. This includes the astrophotos I've taken during those visits. 

 

Joe




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics