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Depth of field and aperture priority (1 Viewer)

wilfredsdad

Well-known member
Hello - maybe somebody could clear this up for me: I have noticed in most discussions about camera settings for digiscoping that aperture priority is recommended. I am assuming that this is because it allows one to set the highest f stop for the conditions in order to try and maximize depth of field. However, isn't the depth of field going to be determined by the current level of magnification in the scope? and therefore, in respect of depth of field, the aperture of the camera lens is going to be irrelevant?
I admit to not really understanding the relationship between the camera lens and the scope and how the camera focuses thro' the scope but I am assuming that the camera focuses on the image which has already been brought into focus (one hopes!) in the eyepiece of the scope and to all extents and purposes that image has no depth (it's flat?) and if so whatever you do with the camera lens is not going to increase or decrease depth of field? Or, then again, maybe I have got it all wrong - anybody out there could explain to me? kindest regards to one and all.
 
Compact cameras with small sensors have diffraction limitations starting at just after F5 or so. F4 is the sweet spot for my last 3 digital cameras (mid level to prosumer models - not cheapies). The auto mode of my Fuji F30 likes to use apertures as small as F8. It's very frustrating. Other modes are better for this issue. Unfortunately when conditions are too bright, it's also limited by the 1/1000 shutter.

I don't have any comments on the affect of camera on dof of the scope/ep system but I would guess that the scope is the limiting factor rather than the camera.

Matt
 
I did some experiments with camera lenses on a dslr photographing through an eyepiece and going from say f1.8 up to f16 only increased the depth of field by around 3 inches so it had a minimal effect on the photo but it does have some effect. It's not really enough to be of use though. With a point and shoot camera you really need to be wide open to get the fastest shutter speeds so again you wouldn't likely want to stop down the lens.

At the moment I shoot prime focus with an astro scope and dslr and with this method you can greatly increase the depth of field by covering the front objective lens with something that has a smaller hole in it. This is basically performing the same job as the aperture blades in a lens and this allows you to control how much of the background is or isn't in focus.

Paul.
 
Ah! - firstly, thanks for the replies - so am I right in thinking then that the actual reason to use aperture priority is to set a large aperture in order to capture as much light as possible and thereby obtain a fast shutter speed? Actually, so far in my digiscoping I have tended to use shutter priority, my logic being that I can set a speed which will be fast enough to avoid motion blur (125th or faster) and let the camera look after aperture. I reckon that if a picture is a bit dark you can do something about it later, but if it's blurred due to the bird moving (and the the pesky little critters do tend to jump about!) then it's useless. At the moment I'm still experimenting but I have so far learned the following: 1)Get as near as you can 2)Only go out on bright days (actually very thin cloud with a high sun behind it seems to be best) 3)Take lots of pictures! I suspect that most of you guys learned all this a long time ago. For the record, I am using a Celestron Ultima 100ED scope (after a lot of reading I came to the conclusion that when it comes to objectives for digiscoping size does matter) I have so far been using my Fuji E550 which is a good little camera and I was able put it straight on the end of the eyepiece (which has a T2 thread) with the Fuji adapter. However, I have just got a Canon A570IS and have ordered an SRB-Griturn swing out adapter bracket. One thing I learned with my experiments with the Fuji is that relying on the camera screen for focusing the scope is very dodgy - things could look really sharp on the screen but infact be badly out of focus when looked at in my PC. I found that when I focus the scope by eye and then fit the camera and shoot I seem generally to get much sharper pics - this process should hopefully be a lot easier when I get my swing out bracket. When I have got things sorted I hope to post some pics. Regards
 
You want to shoot aperture priority if possible so you will have more shutter speeds available for proper exposure at any given ISO. You increase/control shutter speed by raising ISO values.

As for focus, you can manually focus with scope to get you close enough so that the camera autofocus can then lock on for that extra bit of sharpness. You may find with your camera that setting focus to Macro mode will allow faster, more reliable locks. This is a good way to shoot with the camera on a swing-out adapter.

The completely manual method is to switch your camera to manual focus set at infinity and use the manual focus of the scope. Full manual can be really hard on small targets at distance so best to zoom in as far the cameras optical/digital zoom will allow to get focus then back off enough to frame the subject and avoid vignetting and slow shutter speeds.

hope this helps,
Rick
 
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DOF is very shallow and mostly determined by the scope. With a P&S I set the camera to Aperture priority. Because fo the small sensor size of the P&S, noise is a problem (Noise ninja and other noise reduction software helps). With a DSLR, I set the camera to manual mode and manual focus, usually close to or at infinity. Most of the time, with the DSLR, my aperture is optimum at f3.5 or f4.
 
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