Night sky movement..

peter k. said:

Nah.. don't want straight star trails.. don't want any trails but the meteor trail...

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Ah! I understand now.

Easiest way to get what you want: Look up how to make a barn door tracker. Yes, that's really a thing in astrophotography and it's meant to do exactly what you want to do. They even use one on the space station.

Here's the formula for determining star trail length along the celestial equator where apparent star motion is greatest:

L = F x E x 0.00007

where

L= trail length (in same units as F)
F= focal length
E=exposure time in seconds

Depending on the resolution of the lens and degree of enlargement of the final image, this works out to approximately the following for trail free images with a 50mm lens:

13 seconds, for a star at declination of 0 to 30 degrees
25 seconds, for a star at declination of 30 to 60 degrees
42 seconds, for a star at declination of 60 to 90 degrees

Hope that helps.

Thomas

Nodda Duma said:

Ah! I understand now.

Easiest way to get what you want: Look up how to make a barn door tracker. Yes, that's really a thing in astrophotography and it's meant to do exactly what you want to do. They even use one on the space station.

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Yup, I started with one of those, and a watch and wrench. Worked well.

Barn Door Tracker.. yea I looked those up and checked them out this morning,. but first well see if were into the "Dark Night' stuff... St John of the Cross while we wait on exposure, or Star Wars, as the heavens slip by... :alien:

If you have a simple exposure guide like Kodaks.
A sample exposure given with ISO 100-400 films uses 10min to 1 hour @ f1.4-f4. Fer sure star trails will be there.

But, You could use exposures short enough to minimize the trails by making multiple exposures. You're going to
burn film anyway why not use a smaller format to get a baseline before going LF?

Well John.. cut a 4x5 in half.. now I'm @ 120 and took two shots.. using an exposure guide I got off the web, shot wide open.. first one for 30sec the next for 60sec
The reason I'm using LF is so I can develop as I learn, and make changes, rather than shooting a roll.

Ignore what I said about pushing, I wasn't thinking straight. You can use push development but don't use push metering. It didn't register that you won't be metering at all so when you said @ 1600 I thought you'll lose two stops of exposure which you don't want to do.

Some extra film development(dev push) may help but you will need to experiment to find how much is good. If you are scanning for print then I doubt you need to dev push as you can adjust in post. But if you intend to wet print then it may help.

From experience with ISO 1600 and a 24mm/2.8 lens, 20-30 seconds is about what you can do without getting noticeable trails.

BUT: consider that meteors are typically brighter and shorter duration, and in a different direction than the star trails, so you might want trails as a backdrop for the meteors.

Meteor trails with star trails = equatorial mount + to know where to point the camera. Too, don't expose too long if you live in a light polluted area...

Unwanted light, from man mostly, can be annoying in these exposures. I had a cunning plan to get the Perseids reflected in a lake, but instead the tiny back-door light of the cafe next to the lake made a nice(?) shimmer on the water and washed out any meteor trails. With half an hour exposure and a 35mm lens (on 6x6) the trail effect is small but noticeable. Nice but not what I was after, at two in the morning.

Update.. this has been allot of fun and educational... two nights ago we had some cloud cover come in, and I tried with the lens wide open.. one @ 30 seconds and another @ 1 minute.. anyway. Just to see if anything would appeared. Even if it where blurred.
I had cut a 4x5 sheet, to make two MF negatives, and then used an old exposed 4x5, that I had cut up, to fill in front and in back of the 'live' MF size negative, so that it would sit in the middle of the 4x5 holder, and stay locked in.
Well we developed the two, HP5+ in D-76 for 18min for a 1600 ASA exposure, and couldn't really tell, if I had any stars at all, as there was no reference for the exposure, as I was shooting at the Azimuth, and angle recommended by the site. There was no surrounding foliage or silhouettes. DA.. concentrating so much on the sky, forgot the rest of the story. Ha... so the spots on the negative, that I had, I could not tell if they where just dust or what. But I suspect there was nothing.
Last night, again tried.. and the night was clear, and this time with the naked eye could see many more stars, yet looking on the ground glass.. could see nothing!!! When I moved the camera to the big dipper I could see some faint light.. but that's not the direction that they recommended. So set the camera back, Azimuth 316* Altitude 50.5*
Now normally one would use a wide angle lens for night shooting, and that makes allot of sense, but I'm wanting to see how much of the night sky these, two 35cm/12.5 Protar Ser. Vll cells, will cover, as combined they make, a 205/6.3 lens.
Why, because if the meteorite shower is a good one, and if I can get still back round stars, it will make a better shot.. me thinks.. one crazy man's opinion. That's if I'm lucky and a meteorite shows up in the correct space and place!
So last night I shot two shots again.. and wanting to be sure to get an image.. shot for 14 minutes for the first and 7 minutes for the second.
We got tails.. But tails is not what I want, but as shown below,for the 7 minute one, they are strong and bright, and a lot less confusing then the 14 minute exposure.
Now remember I couldn't see any light of the stars at this location on the ground glass, so although its a no nothing shot.. the film saw it.. and that's what counts, so on to the next effort. What crazy fun,

now you have a negative and scan you can measure the length of the trail and divide by 7 to find out how long the trail will be for 1 minute etc. So you can work out how much time will give you a spot instead of a trail.

Measuring from your image and assuming exposure was 7 minutes, then I would guesstimate 18 seconds should be close to correct to give you a point instead of a trail. 30 seconds should make it a bit brighter.

Ok RobC your about right... last night to verify, shot a formation that could be identifiable in photo, Cassiopeia, @ 30sec.
Here are the results.. this gives me some confidence, lof what I'm trying to do can be done. But boy, on real negative will have to use distilled water, not only in the photo flow, but the developer and rinse. The hard water I have here really shows up in these shots.
Note in the zoom you can see a little movement.. which is great as it allows one to notice and take out dust and water spots.

I think they're pretty good for first attemps. I can see stars are slightly elliptoid. I'm sure it will get better as you nail the time for that particular focal length. I still think for best sharpness you will need that 1/2 to 1 second but that may not give much of an image cos it'll be so dim. I rekon that 18 seconds will be about best compromise for brightness with minimal motion..

Yes hard water is a pain.

Maximum acceptable exposure time depends on the angle of view of your lens.

there is the little mater of actually having the shutter open when the meteor appears. So I guess a really short exposure is pretty much out of the question unless you happen to get really lucky.
I don't know about this particular meteor shower. Do they give any predictions for how many meteors per minute or hour are expected?

On the basis of my experience doing the opposite — recording star trails over 6 hours or so down here in Australia on Provia 100F, to record the night sky without any movement of the stars requires an exposure shorter than 15 to 20 seconds with a fairly wide aperture, say f5.6 to record detail. This is also true using digital aparatus, and is often enhanced by layering as an alternative to multi-exposure, which is another analogue technique worth experimenting with.

RobC said:

there is the little mater of actually having the shutter open when the meteor appears. So I guess a really short exposure is pretty much out of the question unless you happen to get really lucky.
I don't know about this particular meteor shower. Do they give any predictions for how many meteors per minute or hour are expected?

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Yes it will be a matter of luck... and the predictions are slight.. but as stated

October 8, 2015, the Draconids
The radiant point for the Draconid meteor shower almost coincides with the head of the constellation Draco the Dragon in the northern sky. That’s why the Draconids are best viewed from the Northern Hemisphere. The Draconid shower is a real oddity, in that the radiant point stands highest in the sky as darkness falls. That means that, unlike many meteor showers, more Draconids are likely to fly in the evening hours than in the morning hours after midnight. This shower is usually a sleeper, producing only a handful of languid meteors per hour in most years. But watch out if the Dragon awakes! In rare instances, fiery Draco has been known to spew forth many hundreds of meteors in a single hour. In 2015, the waning crescent moon rises at late night and will not intrude on this year’s Draconid shower. Try watching at nightfall and early evening on October 8 and 9.

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Yes, and I'm also have the thought of using the one I've been testing.. for 'luck' and setting up the 3x4, for a long exposure... as I have used that camera before back a year or two ago down at Lost Dutchman State park.. for a night star trails shot.