Setting dslr+telescope focus in the daytime.

[NIGHTBOY]

Is it possible to set the focus to infinity in the daytime with a dslr connected to a scope? Lets say you focus it on something 2miles (maybe more) and then mark the outer focuser tube so you know when your on that mark at night you are actually focused at infinity. Would different seeing conditions etc mess things up??

[nmoushon]

Yes you can do that. Try and pick the farthest possible object to focus on. With in reason of course. You need to be able to see if its in good focus or not. But the night temps will change the focus point. You'll be close but you will need tweaking once the camer/lens adjust to the change in temperature.

[Dave_D]

i've read a few threads that say it wouldn't work. better off using something like a bahtinov mask that are cheap enough to buy, or (like i did) simple to make with a bit of time and patience. if your dslr has something like live view you can focus on a star with the bahtinov in place and then remove it and know you have pinpoint focus.

[Leveye]

Not unless the moon is out or you use a solar filter on the sun.

[Bizibilder]

It is well worth marking your focusser tube for common set-ups - it can save quite a bit of time.  You won't get perfect focus with a felt pen mark but it will be near enough so that just a final "tweak" is needed.  As suggested a Bhatinov mask is really useful, if not essential.

[NIGHTBOY]

What do you make your own out of??

[Naemeth]

What do you make your own out of??

Here you go

http://astronomybox.blogspot.co.uk/2012/08/tutorial-diy-bahtinov-mask.html

Or

http://stargazerslounge.com/topic/29909-diy-bahtinov-mask/

[NIGHTBOY]

Great stuff thank you.

Say your using a dslr and scope and you've set your focus using the mask, if you add a Barlow do you have to re focus or will it stay the same?

[Alveprinsen]

What do you make your own out of??

Dude, just get one online.

They're dirt cheap.

Here's one from First Light Optics, starting at 13.95£ going up to 33.95£ depending on size.

I got one from www.spike-a.com for my Skywatcher 180 Pro Maksutov. They're a bit more expensive though, but they are in metal while the ones from FLO are some kind of plastic or whatnot. They both do the job though, so there is really no difference other than the physical feel. I like metal tho.. But still, I've ordered a bahtinov from FLO for my Skywatcher Explorer 200P DS which will arrive this friday. I also got one for my Evostar 80ED Pro... Works like a charm.

If your camera is too weak to pick up a star "live" on live-view, just set your ISO setting to like.. 3200 or whatnot, and 10 sec exposure time. You will get kickass spikes. Its what I do... Klick - zoom and check spikes, ajust focus, klick again, zoom and repeat.

Sincerely, Alveprinsen.

[Sandancer10]

I have live view on my DLSR and use the Moon or Jupiter if the Moon isn't up. I zoom in and set the focus and then zoom out to take the picture.  I've found this a quite good for taking Planets etc., but I've bought a Bahtinov Mask for DSO to try and get a sharper result.

Brenda 

[lensman57]

Is it possible to set the focus to infinity in the daytime with a dslr connected to a scope? Lets say you focus it on something 2miles (maybe more) and then mark the outer focuser tube so you know when your on that mark at night you are actually focused at infinity. Would different seeing conditions etc mess things up??

Hi ,

Setting the focus for AP using terrestrial focus methods is just useless. You need to set the focus  of your scope - imaging set up once it has reached thermal equlibrium after cool down. This actually changes even after equilibrium due to further temp changes and fluctuating humidity but for the purpose of our hobby the first correct focus is sufficient enough. You will never be able to duplicate an imaging or observing condition in the cold of the night during daytime, at least not outside of a lab. If you have a laptop I suggest that you download trial version of APT which is fully functional and not time limited ( the licence is only about £10.00) and learn to use the FWHM focusing of a star using the live view function of the camera. Check the imaging section and you will see that this is what most of us use to obtain critical focus for DSO imaging and the results speak for themselves. FWHM only works with point sources of light, stars, but you can use it to obtain critical focus on a planet by using a nearby bright star, and I mean nearby as the elevation of the star has to be similar to the planet to account for the thickness of the atmospher as this effects the focus to a great degree. Last year while I was learning imaging and going for Saturn I used Spica to get the focus right and then slew to the nearby target. Take a bit of time and learn to do things the correct way, soon it becomes so quick that you wonder what the fuss was all about. APT only works with Canon DSLRs ( native e support ) and some CCDs through the Ascom platform BTW.

A.G

[NIGHTBOY]

Just looking at the bahtinov masks, is the 200p f4 5 or 6,???

[Steve Ward]

f5 .

Try here for masks , http://www.morris-engraving.co.uk/bahtinov.htm , super accurate , laser cut , great value and a nice bloke too ... 

[glowingturnip]

agree completely that there's no shortcut to be obtained in setting a focus in the daytime to use at night.

One exception though, for moonrises and the like, they move so quickly you haven't got time to set focus properly before it's left the horizon.  I set the focus for this shot on trees about 3 miles away (the trees in the shot are about 1 mile away), half an hour before moonrise:

[NIGHTBOY]

Wow that's an awsome shot gt, was that taken in the uk??

[glowingturnip]

nah, spain - was this year's super-moon

[NIGHTBOY]

Lovely shot mate. I prefer these single snapshots to all this stacking business, they just look so more natural/real. Great effort well done, love it.

[glowingturnip]

cheers mate 

[Steve Ward]

You really need to persevere with the stacking , you'll never get crisp detailed , noise-free 'close-ups' without.

Specifically timed / located shots like the great shot of the Moonrise obviously can't be stacked without smearing the foreground but when there's just a 'black' background it's the way to go.

But even 'snapshots' like this require a great deal of planning as far as finding the location to shoot from , exposure and f-stops , ISO settings etc , etc ... 

Like everything in this game there's a learning curve to climb , no easy way round it I'm afraid.

[NIGHTBOY]

I'm pretty handy with my dslr, just not when it's attached to a scope... Hehe.

Love night shots with the forground in them, just something about them.

[glowingturnip]

that one was through a scope though ;-).  Mad scramble to get the exposure right before the moon rises too far, and remember to be hands-off before firing the shutter !

[NIGHTBOY]

Looks clear tonight so I'm going to have a [removed word] about with the dslr and 2x Barlow on Jupiter, will probably result in a hour in the cold for nothin hehehe.

[Leveye]

agree completely that there's no shortcut to be obtained in setting a focus in the daytime to use at night.

One exception though, for moonrises and the like, they move so quickly you haven't got time to set focus properly before it's left the horizon.  I set the focus for this shot on trees about 3 miles away (the trees in the shot are about 1 mile away), half an hour before moonrise:

Your focus here is most def not on the trees. I'm a bit confused. Awesome shot all the same.

[glowingturnip]

nah, the trees I focused on were about 3 miles away, those ones are only about a mile away on a nearer hill.  That is one thing that bugs me about that photo, would be nicer if I could stop my scope down for a wider depth of field and have the trees in focus too - can you do that ?

You might also notice that north on the moon isn't north in the photo - it's actually a hillside, 20 or 30 degrees down from left to right, but thought it looked nicer like that.  I had to crop out the lamppost that was clearly at a wrong angle though !