Old 16-11-2007, 11:25 PM
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Location: Perth
Posts: 51
Is it possible to do unguided with film?

I have ordered a Tak Sky 90 and p2z. That was my budget, since then I've gone over by ordered the field flattener and camera bibs and bobs.

Now, using a Mamiya 645 on a Sky 90 @ f/4.5 with a p2z @ a periodic error of 8 (+- 4). If I do a drift alignment etc.

How long can I expose the film for unguided given that a 400mm focal length and a period error of 8? Will it be long enough to get an image?

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Old 17-11-2007, 05:42 AM
Dazzled by the Cosmos.

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Join Date: May 2005
Location: Brisbane
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Can’t answer your question specifically, but I do recall that when using my polar aligned Vixen GPDX mount fitted with my Pentax KM 35mm SLR, I could take 10-15 min unguided exposures with 135mm and 200mm telephoto lenses.

You should be able to take longer exposures near the South Celestial Pole (smaller arcs of movement) whereas nearer the Celestial Equator, the stars make larger arcs in the same period.

When I first started 35mm film astro photography, I found Astrophotography for the Amateur by Michael A. Covington an invaluable book.


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Old 17-11-2007, 09:11 AM
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Hi Daniel,
According to the books I have 10 arc sec of movement would be just detectable with a focal length of 500mm so you should be OK with 8 sec at 400mm as long as you have a good polar alignment I can`t see why you couldn`t go 10 min or longer? But I suspect you would get a fair share of rejects amongst the good ones without any guiding..
Good luck!!
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Old 17-11-2007, 10:48 AM
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Kal (Andrew)
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Location: Sydney
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There is a good review of your mount here, and if you click on this link in the review you can see many samples of astrophotography using the same combo you have (Sky 90 @ F4.5). This user seems to have no problems doing 2 minutes unguided (on film) and in some cases he goes longer.

Looking through his astrophotgraphy gallery is pretty impressive I must say
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