twinkle twinkle little star

[devilgas]

yay, cloud free evening. managed to get outside and have another crack at the orion nebula.

the following image is a 1 minute exposure at iso 400. not the best way to capture an image (should really be stacking multiple images), but was testing the tracking on the scope. seems fine to me

[devilgas]

Re: twinkle twinkle little star

a bit of an improvement from the one with the old 'scope.....

[Pol]

Re: twinkle twinkle little star

A cracker and lovely to see all those other stars too. Definitely an improvement on the one from your old scope.

Pardon my ignorance, Dave, but how come there's no 'earth/star movement' visible in the stars despite the one minute exposure. Is that because of the magnification + tracking or what? An idiot's guide please or I'd be lost.

Pol

[Pops]

Re: twinkle twinkle little star

Stuff we only usually see in mags. Looks brilliant

[devilgas]

Re: twinkle twinkle little star

A cracker and lovely to see all those other stars too. Definitely an improvement on the one from your old scope.

Pardon my ignorance, Dave, but how come there's no 'earth/star movement' visible in the stars despite the one minute exposure. Is that because of the magnification + tracking or what? An idiot's guide please or I'd be lost.

Pol

the 'scope i now use has a motorised mount which follows the stars as the earth rotates. last night was more an exercise in checking the scope over, checking my polar alignment (the more accurate this is, the less the tracking will 'drift') and seeing how accurate the tracking was. 1min exposure was about the limit before noticeable star movement can be seen, which i'm quite happy with.
if the mount wasn't motorised, the stars would just be streaks across the entire frame.
i was shooting at something called 'prime' (no eyepieces used) which means it was shot using an 1100mm 'lens'.

[Pol]

Re: twinkle twinkle little star

the 'scope i now use has a motorised mount which follows the stars as the earth rotates. last night was more an exercise in checking the scope over, checking my polar alignment (the more accurate this is, the less the tracking will 'drift') and seeing how accurate the tracking was. 1min exposure was about the limit before noticeable star movement can be seen, which i'm quite happy with.
if the mount wasn't motorised, the stars would just be streaks across the entire frame.
i was shooting at something called 'prime' (no eyepieces used) which means it was shot using an 1100mm 'lens'.

Thanks for the explanation. I thought maybe it might be because of the tracking and it certainly seems you've got the timing spot on if that picci is anything to go by. Those stars look pin sharp - an excellent quality image imho.

I hadn't realised you didn't need an eye piece either. So it seems you have top-notch kit there. Well worth the cost.

Pol

[devilgas]

Re: twinkle twinkle little star

you can use eyepiece projection to get higher / lower magnification, but it introduces more defects into the light path and impacts on the light transmission. i'll be honest and admit that i used to do this until i was told the error of my ways
i'm fortunate in that the scope i chose was enhanced for photography - allowing a closer focusing distance - which allows me to shoot at prime.

as an example, i took a photo of the moon last night. at prime, the moon takes up about 1/2 of the image (with pin sharp detail as the light path only has the atmosphere & 2 mirrors between the moon and the dslr sensor). if i use an eyepiece, i can get higher magnifications, but the exposures become longer. for a bright object such as the moon, this isn't a problem. for fainter nebula it makes life a bit more difficult.

[Pol]

Re: twinkle twinkle little star

you can use eyepiece projection to get higher / lower magnification, but it introduces more defects into the light path and impacts on the light transmission. i'll be honest and admit that i used to do this until i was told the error of my ways
i'm fortunate in that the scope i chose was enhanced for photography - allowing a closer focusing distance - which allows me to shoot at prime.

as an example, i took a photo of the moon last night. at prime, the moon takes up about 1/2 of the image (with pin sharp detail as the light path only has the atmosphere & 2 mirrors between the moon and the dslr sensor). if i use an eyepiece, i can get higher magnifications, but the exposures become longer. for a bright object such as the moon, this isn't a problem. for fainter nebula it makes life a bit more difficult.

Interesting stuff.

David has a Meade 90 with a load of eyepieces somewhere around here but he hasn't used it for years and I don't think I ever saw any pics from it (I think he has/had a Nikon Coolpix with a mount iirc).

I wish he'd show it to me in use but he just keeps saying "the light's no good around here" and says it's too big for carting about when we're away in the camper. Such a waste!

PS ... I can imagine your picci of the Orion Nebula as an interesting CD cover picci

Pol

[devilgas]

Re: twinkle twinkle little star

Interesting stuff.

David has a Meade 90 with a load of eyepieces somewhere around here but he hasn't used it for years and I don't think I ever saw any pics from it (I think he has/had a Nikon Coolpix with a mount iirc).

I wish he'd show it to me in use but he just keeps saying "the light's no good around here" and says it's too big for carting about when we're away in the camper. Such a waste!

PS ... I can imagine your picci of the Orion Nebula as an interesting CD cover picci

Pol

you should dig it out.

for longer exposure photo work, you may need to make some mods depending on which scope it is. if it has a glass front element then it's probably one of the ETX series. these are great for visual use but need some modification for long exposure photography - they use an Alt-Az mount (up-down / left-right) which makes it easy to find stuff in the sky. the thing is the sky rotates around the celestial poles (roughly where the north star is), hence why star trails are curved. so, the scope tube also needs to rotate at the same rate. an alt-az mount will track things no problem, but it cannot rotate the tube. this can be easily fixed by inclining the whole telescope so that instead of it being in Alt-Az mode, it works in equatorial mode.
it takes a bit to get the head around the subject, but once it clicks it makes perfect sense.

[devilgas]

Re: twinkle twinkle little star

says it's too big for carting about when we're away in the camper.

might not be the etx90 then as they are quite compact and easily transported.

[Pol]

Re: twinkle twinkle little star

It's the ETX 90. I've been on at him about it this afternoon and 'encouraging' him to dig it out and set it up again, even if it's only in the back or front garden. He's been resisting saying there are too many street lights but I think maybe he's weakening. I have a particular location in mind down on the Romney Marshes on a farm where we can sometimes stay overnight. I can be very persistent (aka a right pest).

I'd never be able to get my head around it myself and David always blinds me with science, never uses 2 words when 200 would do, but I would still enjoy just having a look, even without taking any pics.

He's just said "I think maybe I'll get it out and get used to using it again". I've even gone so far as to pack 4 warm fleece blankets and spare Duvets in the 'van. So fingers crossed he might be inspired to get going again.

Yay.

Pol

[Barr1e]

Re: twinkle twinkle little star

Thanks for posting the 'little star' - and thanks for the explanation to Pol, it covers much.

Fascinating.

Regards. Barr1e

[devilgas]

Re: twinkle twinkle little star

@pol....

iirc, the etx90 is quite a slow scope (about f13) which means for deep sky objects (dso's) it will struggle. for planets, the moon etc, it will have no problems, so light pollution on these targets also won't be a problem. i'm not saying that it can't be used on comparitively much fainter DSO's, just that it will be a lot harder to image them. seeing them with the eyes though is a different matter. i remember the first time i truly saw the orion nebula - i'd attached an oxygen iii filter to the eyepiece - and it was unforgettable. adding a matt black shield around the end of the scope will also help to reduce the effects of unwanted streetlight entering the scope.

another thing you can try with the 90 is to attach a white light solar filter. you won't get the images that i've been posting as shot through the PST - they're in a very specific light band - but will be able to get great views & shots of sun spots.

[Pol]

Re: twinkle twinkle little star

@pol....

iirc, the etx90 is quite a slow scope (about f13) which means for deep sky objects (dso's) it will struggle. for planets, the moon etc, it will have no problems, so light pollution on these targets also won't be a problem. i'm not saying that it can't be used on comparitively much fainter DSO's, just that it will be a lot harder to image them. seeing them with the eyes though is a different matter. i remember the first time i truly saw the orion nebula - i'd attached an oxygen iii filter to the eyepiece - and it was unforgettable. adding a matt black shield around the end of the scope will also help to reduce the effects of unwanted streetlight entering the scope.

another thing you can try with the 90 is to attach a white light solar filter. you won't get the images that i've been posting as shot through the PST - they're in a very specific light band - but will be able to get great views & shots of sun spots.

Thanks for all these explanations and help, Dave. I really appreciate it. I read all of the above to David and he says he knows and understands but needs to get filters.

Looking and seeing things is what I'm most interested in rather than taking pics so that's mainly what we'd be aiming to do. I'm ever so chuffed to report that he's now promised to get it out again and set it up soon. We're also planning on taking it down to the marshes when he's familiar with it again.

I really appreciate the inspiration to do summick a bit different, thanks.

Pol

[devilgas]

Re: twinkle twinkle little star

Thanks for all these explanations and help, Dave. I really appreciate it. I read all of the above to David and he says he knows and understands but needs to get filters.

Looking and seeing things is what I'm most interested in rather than taking pics so that's mainly what we'd be aiming to do. I'm ever so chuffed to report that he's now promised to get it out again and set it up soon. We're also planning on taking it down to the marshes when he's familiar with it again.

I really appreciate the inspiration to do summick a bit different, thanks.

Pol