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Beginner workflow for star tracker

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#1 berkanxj

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Posted 11 October 2020 - 07:06 PM

Hey everyone, just bought a Mamiya 645 for me and my girlfriend to use for regular photography. Quite popular these days it seems… Anyway after doing some research I’m thinking about mounting it on my star tracker for astrophotography. My setup now is: Star adventurer, Canon eos 800D and 200mm Takumar lens (also have an 8inch dob). The Mamiya came with the 80mm 2.8 lens.

So my plan is to mount the Mamiya like I would with my dslr. Adding a guiding setup (ASI120MM MINI + Guide scope) for guiding and polar alignment through Sharpcap.
I know a real mount like the HEQ5 would be way better, but it’s too expensive for me at this time sadly.

Will this work? I’d like to try North America nebula, Orion, Pleiades, California nebula, … Let’s say I would like to photograph the Orion Nebula. I’ll do my polar alignment, turn on bulb mode and use mirror lockup and a cable release. What film is being used these days for AP that’s available to me? I’ve read about Kodak E100 and Fuji Provia 100F. Also, how do you frame your picture? Are the stars bright enough through the viewfinder? Another downside of star tracker is the lack of GoTo system, so my framing will have to be spot on, but at the same time this isn’t impossible at the 80mm focal length, right? Usually I take multiple shots for framing on my DSLR but that’s obviously not possible here.

How long should/can my exposure be for ex. Orion Nebula at F4 80mm. I’ve seen someone do 80minute milkyway exposure and someone else 15minute exposure on Orion, so really no clue. I know, a lot of questions but I’d really like to try this, but as you can tell I’m a total noob at film. Please help with my workflow or link me some relevant posts if you have time, thanks!



#2 TxStars

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Posted 11 October 2020 - 09:45 PM

With Kodak E100 or Ektar100 around 20 min @ f/4 depending on your sky conditions (go longer if you have dark skies and shorter if you don't)

For brighter objects a shorter exposure will show the inner regions better where a longer exposure will show outer regions better.

There is no "One perfect" exposure time to use each one will show a bit different ..

When you start your exposure use a loose fitting cap or black card as a hat trick on the camera lens to reduce any vibrations from opening the shutter.

 

And welcome to the dark side...



#3 berkanxj

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Posted 12 October 2020 - 01:49 PM

Thanks I'll give it a try soon. So Ektar100 with the first and last photo being a daylight photo right? easier for framing. I will be getting it developed, but when I read "push +1 or +2 stops during development" is this something I can ask or?



#4 TxStars

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Posted 12 October 2020 - 11:29 PM

When giving film to a lab I always tell them "Do Not cut" and then later do it myself using a loupe or viewer on a light box or light table.

And yes you can ask for "Push processing" , tho you may not want to do this on the first roll.

Shoot one roll and have normal processing done that way you can get a base line of your local conditions and scope / lens combo.



#5 Giorgos

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Posted 22 October 2020 - 03:43 AM

I'd suggest to use black and white film and develop it at home with a moderate to high contrast developer. Ektar 100 gives a very strong blue cast on long exposures that you may not like... Also Ektar 100 and E100 slide are very expensive. Start with 400 ASA film and 20 min exposures at f/4 from a DARK site. If you live under light pollution just forget film astrophotography. Kodak Tmax 400 and Tri-X, Ilford HP5 and Ilford Delta 400 are good films to try. Delta 400 is also sensitive to red but you will need a red filter and long exposures to take advantage of it. Keep notes about exposures, apertures etc.  Guiding is barely needed with a normal lens provided you have achieved a good polar alignment. For 35mm shooting with 200mm telephotos I find EASIER to manualy guide with an illuminating reticle eyepiece checking the guide star every 1-2 minutes than setting up a autoguiding rig with guidcam, laptop etc.


Edited by Giorgos, 22 October 2020 - 03:46 AM.



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