Posts Made By: Joplin Motisher-Chittenden

I couldn't agree more - I pondered posting the shots of the Norther Flickers below for quite a while. I was still in high school when I shot those and I couldn't afford anything better than the Meade maksutov scope (which I suspect had bad optics even compared to other similar scopes - much worse than any of the ETX series). Now I've got a an 80mm fluorite apo that is perfect for the purpose and I just purchased a used Coolpix 995 so I will soon be posting some better images.

Jim,

While I haven't actually done much digiscoping yet, I will take a stab at this one. I do know a fair bit about afocal photography. Determining the effective focal length of the scope/ eyepiece/ camera combination is the easy part. You've got a 480mm f.l. scope w/ an 18mm eyepiece which yields 26.66x you then multiply that by the focal length of the camera (I'm going to use the 35mm equivalents), 38 - 155mm. So you get the equivent of a 1013mm to 4133mm lens in 35mm format. Now you can simply divide that by the aperture of the telescope (80mm) to get the effective aperture. In this case we get about an 1013mm F 12.7 to 4133 F 51.7 These should be approximately the right values excluding light loss from lens elements in the light path which should be minimal. Here is where things get kind of muddy the scope/ eyepiece you have yields a 3mm exit pupil which happens to be almost exactly the same as the true aperture of the camera's lens when it is set to wide angle so, in theory it really is operating at f 12.7 so if you close down one f -stop, you will be at f 18, etc. At the full zoom setting though, the true aperture in the camera's lens is about six millimeters so it is effectively not using 3/4 of the light from the scope, reducing the maximum effective aperture of the system from f 51.7 to f 103.4 I have noticed that, with the coolpix cameras (I used a friend's 4500 for some afocal planet shots) the high zoom settings result in a really, really dim image and this would seem to agree with the results above. The easiest way to check this would be to aim the camera/ scope setup (set to f2.6 , aperture priority) at a gray card on a sunny day, normal exposure at ISO 100 setting would be F16 so you should get a reading of about 1/150 sec at the f 12.7 effective aperture. The reading at maxium aperture zoomed all the way out should be about 1/4 sec.

I would note that, at the extreme focal lengths we are talking about, no amount of reducing aperture is going to give you much depth of field, so you might as well use wide aperture to keep the motion bluring of the subject and camera to a minimum.

Joplin

I rember a post (but I wasn't able to find it via a search) on Astromart regarding the thickness and weight of these tubes. The person was noting that the tube he got from them weighed 50lbs and was way too heavy (it was for a 10" scope). Their website lists the thickness for that tube at .4" which is way too thick considering the weight of the material. Aluminum tubes will be far less heavy than these resin tubes and will have superior thermal conductivity. The only practical sizes for these resin tubes are the 4.25" size and possibly the 6" size, but even those will be quite heavy compared to a standard aluminum tube.

Joplin

Jim,

It looks like there was probably a bit of subject or camera movement; it's possible the bird shifted right at the moment of exposure. At this high of a magnification you will need a really fast shutter speed (at least 1/250 or 1/500 to stop any movement), even when using a tripod. Also a remote release will help a lot by isolating the camera from any vibrations that might be caused by your finger on the shutter release. It's still a nice shot though. I just got my used coolpix 995 by UPS today, spent most of the evening experimenting with it and learning the various functions. Once I get the adapters I will try to get some decent bird images and post them here.

Joplin

Great image Tyler, it really conveys the Egret's concentration on fishing well. I also like the fact that it shows a lot of the surrounding environment.

Joplin

Pretty neat - it's too bad that the time increment is so wide, would also be neat if it had an option to animate it. The only other similar resource that I can think of is the Canadian Meteorlogical Center's Clear Sky Clock. It provides more detailed info but is harder to interpret at a glance.

Clear Skies,

Joplin

Your best bet is to go to a professional lab. Be sure to tell them in advance that you want the film "uncut" and "long sleeved". If you just plan to scan the images, you will save some money by getting the film "processed only" , "long sleeved" and uncut.
You will need to cut and sleeve film yourself - it is the only way to be sure. The long sleeve material makes cutting the film easier since you can do it without gloves if you are careful. I suggest archival sleeve pages such as the "Print File" brand ones that can be put in a sealed binder or file box for storage. Another good tip is to have at least two really obvious frames at the beginning and end of the roll that show the edges of the frame clearly. Two shots of a white wall at either end of the film will help the technician determine where to start cutting. That tip is particularly usefull with slides, where the cut postion isn't easily adjusted once the roll is started (many labs just line it up and basically let the machine determine where to cut for the rest of the roll). The reason to have the frames at the end is that most labs start cutting from the end of the roll.
I have found that cutting my own negatives works great but I prefer to have a quality lab mount slides since they are tricky to mount by hand.

Hope that helps,

Joplin

The exposures times for a lunar eclipse will vary wildly depending on the earth's atmospheric conditions and the exact path of the moon through the earth's shadow. A large amount of bracketed exposures is the best bet for getting good results. Here are some starting point exposure times from a table in an a book I have (I used these once before, with good results) :

1/4 immersed in Umbra shadow - 1/125 sec.

1/2 immersed in Umbra shadow - 1/60 sec.

3/4 immersed in Umbra shadow - 1/30 sec.

Totality - 30 seconds.

I would use the partial phase times as a short exposure starting point, then bracket with several longer exposures for each one. Totality is very unpredictable, I would start at about 4 seconds then work up to at least a minute. You will need accurate tracking for the totality exposures. Also keep in mind that print film is much more forgiving when it comes to exposure accuracy and has much more recording range than slide film - which makes it a lot easier to get some detail in both the shadowed and light part of the moon. Print film will tolerate overexposure pretty well, if you underexpose it, the image will have much more grain and won't print well.


Joplin