[old4570]

I can adjust for wind-age ...

Basically start snapping and work out where the best focus is , even if it means the image is slightly out of alignment ( eye view ) I like taking moon shots and getting the focus on the money is tricky , a split screen will give me the op to get focus spot on ..
Just need to take a bunch of test shots .. ( Split screen was ordered , all of $15 . rather expensive bit of plastic , but as long as it does the job )

[Anvh]

For moon shots you don't even need to look into the viewfinder to get the focus correctly just look at the focus ring and set it on infinity or just before it.

[old4570]

For moon shots you don't even need to look into the viewfinder to get the focus correctly just look at the focus ring and set it on infinity or just before it.

Wish it was that easy ...

[Anvh]

Seems i'm missing something then. ^^;
Could you please explain why it is so hard then?

[JimJohnson]

It can be a bit touchy to truly set a long lens exactly at infinity. Typically the lens is capable of focusing past infinity and the scale on a lens is only a close approximation. Temperature has a lot to do with exactly where the infinity focus point is located. When you point a lens toward a clear night sky, the front element will cool even if the surrounding ambient temperature remains constant. Condensation is a high probability on long exposures and focus may shift. The reason why so many astronomers use heating elements on their telescopes is to keep everything at a constant temperature during observations.

[old4570]

Well , unfortunately @ around 1500mm the slightest breeze can cause vibration , the moon itself moves rather quickly so shutter speed is important , and without a split screen getting the focus just right ( not soft focus ) for a nice sharp shot is hard as the sensitivity of the focus mechanism itself can be a bit tight , 1mm this way or the other and you have a soft focus .. Which is why the need for a split screen ,

You can point a shotgun at a target , but with sights ! you can actually aim .. And a split screen allows you to aim much better for a nice sharp focus and maintain such as you go along ..
Another variable that simply needs eliminating for decent moon shots ...

[Anvh]

I indeed forgot the temperture, it's indeed not a good idea to focus past infinity.
The dof isnt super shallow right or do you actually need to be so accurate?
With 1200mm f/8 the dof calulator is giving me some huge numbers...

[old4570]

With the lens I have , yes .. Its either spot on or its a degree of softness .. And the more the lens is boosted , the more critical it becomes ( 2x adapter )
The split screen will help a lot and remove a lot of guessing

Old 500mm Mirror lens fixed @ F8 + 2x adapter ( + crop factor )

[Anvh]

thanks, got it.
didn't knew it became so critical.