focus, focus

[gdheib0430]

So I seriously sat out tonight and took my first widefield shots before my telescope adapters arrive for my dslr. I still need to process them in DSS but I did look at a few of the shots.

Is it normal for the stars to be a tad blurry or can you get your focus down to get super sharp crisp stars? Probably the right question to ask here is are there any special methods you use to insure your focus is as good as it can be?

Oh I did 15 x 20" ex with 15 dark, flat and bias (understand now if you take dark you don't really need bias shots as bias is incorporated within the dar shots as well).

I did notice one of my 20" exporsures had a little start trail in it but am thinking the tripod might have been bumped. Oh, and will 15 shots be that much less effecient than 20 or should I just stick with the more the merrier? hehe and my dark shots...can they be used for all sets of lights I take during my session? YAY the noob is getting closer to no longer needing advice.

[Dave]

If you were using the normal camera lens then it comes as a surprise that the infinity setting isn't quite set at inifinity, hence the stars being slightly blurred. You will need to find the sweet spot. As you have probably found it is difficult to see anything but the brightest stars in the view finder, and using live view you don't usually see them. I keep taking shots and adjusting the focus depending on what the stars look like on the image once zoomed in. Once I have got focus I use a piece of insulation tape to lock the focussing ring so it doesn't move.

[steppenwolf]

With short focal length camera lenses, the favourite option, a Bahtinov Mask, doesn't really work unfortunately. If possible, take a laptop outside with you and capture the images directly to the computer and view them at full resolution, adjusting the focus between each test shot until you get the smallest star shape - this way you are sure that you are seeing what the camera's sensor is seeing.

[gdheib0430]

kk guys I appreciate the answers and no worries about the other questions I have that info down pretty pat now it is starting to click now.

[steppenwolf]

Oh, and will 15 shots be that much less effecient than 20 or should I just stick with the more the merrier? hehe and my dark shots...can they be used for all sets of lights I take during my session? YAY the noob is getting closer to no longer needing advice.

Considerably more subs can be a case of diminishing returns. Between 16 (something to do with mathematics and algorithms!) and 20 would be a good start as the images will become smoother but detail comes with deeper (longer) exposures. As long as your darks have the same exposure length as your lights you can use them for lights throughout your imaging session.

[gdheib0430]

Yeah I appreciate the info I figured as much...I wont be going for killer detail until I upgrade to an autoguid DOB...probably gonna go with an 8" at 1200mm f5.9 over a 10" 1200mm f4.7 ....from what I have read the 8" will give you a slightly wider view but being the same focal length just as deep with the barlow.

Oh hey I am assuming there really isn't anything out there, but I know the cannon's have mods for Ha correction but are there any for the sony a-series dslr?