300mm lens

[Alien 13]

I believe the key to DSLR imaging is not the ultimate sensor temp but keeping it within certain limits during a run so that darks/stacking etc can work its magic

Alan

[Knight of Clear Skies]

Hi

I wouldn't argue with you! I've only ever used dslrs via APT but have seen the exif temperature rocket. Generally, though, you shouldn't have to focus/refocus very often so it's not a big problem really, just something to be aware of.

Louise

Yes, it's a useful tip. It's very difficult to work out exactly how important things like this are as there are a lot of variables. However, I have found I can image faint-ish objects without worrying about sensor temps. If I was going after fainter targets or using slower optics it might be more of a problem.

[Thalestris24]

Yes, it's a useful tip. It's very difficult to work out exactly how important things like this are as there are a lot of variables. However, I have found I can image faint-ish objects without worrying about sensor temps. If I was going after fainter targets or using slower optics it might be more of a problem.

Hi

I suppose I'm more used to doing long exposures with the scopes whilst battling with heavy lp and bright skies. I just started having a go with a 200mm/f4 lens which overexposes the sky in 45 seconds (without a lp filter) I so wish I had darker skies!

Louise

[laser_jock99]

A 300mm lens is very useful bit of imaging kit filling the gap nicely between short FL telescopes and standard lenses. I tend use mine directly on the mount and unguided. With good polar alignment I can get 300s subs but generally stick to 180s subs. I never use the lens wide open, always stopped down to F4 

Some examples of my 300mm F2.8 Sigma APO lens images.

M8 & M20 Sagitarius 4x 300s

M31 Andromeda 4x 300s

Region of Sadr, Cygnus 7x 180s

[Thalestris24]

A 300mm lens is very useful bit of imaging kit filling the gap nicely between short FL telescopes and standard lenses. I tend use mine directly on the mount and unguided. With good polar alignment I can get 300s subs but generally stick to 180s subs. I never use the lens wide open, always stopped down to F4 

Some examples of my 300mm F2.8 Sigma APO lens images.

Lovely images! But expensive lens, lol

[Atreta]

i like taking pictures with lenses too, i'm considering to buy soon one 300mm lens.

what would be a good, not so costly 300mm lens? vintage or not is ok for me.

Frank

[Ags]

Live view warmup is a good thing... It means the subsequent lights are shot at constant temperature, and then the darks are shot at the right temperature too. This assumes that you are shooting the lights and darks back-to-back with no gaps.

[laser_jock99]

Lovely images! But expensive lens, lol

Not really- it is an older manual focus version for less than £200. Wildlife and sports photographers don't want them any more but they are ideal for astro.

[Thalestris24]

Not really- it is an older manual focus version for less than £200. Wildlife and sports photographers don't want them any more but they are ideal for astro.

Ah, ok - nice one! Would be good to have one but I've not seen any around.

[wxsatuser]

Hi

I wouldn't argue with you! I've only ever used dslrs via APT but have seen the exif temperature rocket. Generally, though, you shouldn't have to focus/refocus very often so it's not a big problem really, just something to be aware of.

Louise

My 60Da seems to stabilise after three shots.

There appears to be a few degrees rise, not more than 5, in the first frames.

It is pretty much stable according to the exif data, even after three or four hours.

Have checked this a few times and it seems it's no fluke, a few degrees to start then stable throughout.

Does'nt seem to matter what the air temperature is and I only have 10second gaps between each exposure,

to allow card write, selftimer and mirror lockup.

[brrttpaul]

Well clear skies last night, set everything up and it was looking good ( got the set up down to a fine art now ).put the camera on checked all my settings ISO etc attached the invalometer, and was eagerly awaiting when these clouds came from nowhere and decided to settle above me, so frustrting as I couldnt stay out long anyway. I definately need a power station though, I have been told to make one but TBH me and electric dont mix im hopeless with it. 

[wxsatuser]

That happened to me the other night.

Rolled roof back got setup, takes about 5minutes, start imaging, three shots........cloud out of nowhere..

First sign was guiding messing about, hard to see the faint cloud but it got thicker, gave up went to bed.

Got up to a perfectly clear dawn.

[Thalestris24]

My 60Da seems to stabilise after three shots.

There appears to be a few degrees rise, not more than 5, in the first frames.

It is pretty much stable according to the exif data, even after three or four hours.

Have checked this a few times and it seems it's no fluke, a few degrees to start then stable throughout.

Does'nt seem to matter what the air temperature is and I only have 10second gaps between each exposure,

to allow card write, selftimer and mirror lockup.

Hi Mike

With liveview on for, say 10 mins, my 1100d will go shooting up to 35+ degrees. It takes quite a while to cool back to 25 deg. I don't normally use liveview so it's not a big problem for me. However, even with normal long exposures (300/600/900s with scope) the temperature rises significantly and builds up if I don't allow a decent cooling time between subs. I have the same effect when taking corresponding darks. Perhaps it's a camera/model specific problem? I wonder what others have observed? I should mention that I image at ambient room temperature which probably doesn't help... Taking short exposures with a fast camera lens doesn't seem to be a problem (though I've only just started shooting with a 200mm/f4 lens).

Louise

[Colinlp]

A 300mm lens is very useful bit of imaging kit filling the gap nicely between short FL telescopes and standard lenses. I tend use mine directly on the mount and unguided. With good polar alignment I can get 300s subs but generally stick to 180s subs. I never use the lens wide open, always stopped down to F4 

Some examples of my 300mm F2.8 Sigma APO lens images.

M8 & M20 Sagitarius 4x 300s

M31 Andromeda 4x 300s

Region of Sadr, Cygnus 7x 180s

Those are really nice pictures, especially the M31. So that's just a camera with a 300mm lens on a mount?

[brrttpaul]

Those photos have inspired me to get out there and try it

[ollypenrice]

I can't say I ever managed to focus a fast camera lens in just a minute. I'd struggle to focus an F7 scope in that time. The focal depth is punishingly shallow so focus is ultra, ultra critical. This Telescope Service gadget made life easier.

Olly

[laser_jock99]

So that's just a camera with a 300mm lens on a mount?

Yes- just a camera, 300mm lens on an EQ mount. With the short FL of 300mm & good polar alignment you can go up to about 5 minutes without guiding. 

It's worth taking time to focus accurately with a long lens though. I use the Bahtinov mask for my ED80.

[Colinlp]

Yes- just a camera, 300mm lens on an EQ mount. With the short FL of 300mm & good polar alignment you can go up to about 5 minutes without guiding. 

It's worth taking time to focus accurately with a long lens though. I use the Bahtinov mask for my ED80.

Thanks, I will give this a go in the autumn when I've built my observatory and saved some dosh for a camera. I really like those pictures 

[laser_jock99]

I can't say I ever managed to focus a fast camera lens in just a minute. I'd struggle to focus an F7 scope in that time. The focal depth is punishingly shallow so focus is ultra, ultra critical. This Telescope Service gadget made life easier.

Olly

Camera lens focusing can be tricky mainly because of 'slop' in the focus ring. What you think are tiny adjustments actually translate into large jumps in focus position!

A trick I use to slow down and stiffen the focusing action is stretch a large o-ring over each end of the lenses' focus ring. The friction thus created damps the rotation of the focus ring enough to make micro adjustments easier. It also helps hold the focus position if you accidentally touch the lens in the dark!

[wxsatuser]

I can't say I ever managed to focus a fast camera lens in just a minute. I'd struggle to focus an F7 scope in that time. The focal depth is punishingly shallow so focus is ultra, ultra critical. This Telescope Service gadget made life easier.

Olly

Got a couple of those.

Have used one on the 200mm but prefer to just tweak by hand and use Liveview to watch for the best focus.

It really does'nt take long with a light touch.

[wxsatuser]

Camera lens focusing can be tricky mainly because of 'slop' in the focus ring. What you think are tiny adjustments actually translate into large jumps in focus position!

A trick I use to slow down and stiffen the focusing action is stretch a large o-ring over each end of the lenses' focus ring. The friction thus created damps the rotation of the focus ring enough to make micro adjustments easier. It also helps hold the focus position if you accidentally touch the lens in the dark!

Both my 200 Ls have a nice action, not to tight or slack.

The Sigma is a bit tighter and holds focus for ever.

[brrttpaul]

Well lsat night I was teased again, 10 o,clock not a cloud in the sky set everything up looking good had to wait for it to get darker, 11 oc,lock darker and cloudier, the frustration with this hobby lol. Few things though star aligning with the camera using live screen was a doddle , so was focusing. I set my target M101 as I knew it was straight up,  The plan was 30 sec subs x 50  ISO 1000. 7 I managed before the clouds came over. But I,m happy in a way its all practise,  Heres a photo , its not great by a long chalk but I was so darn nearly there. I may use the 2x convertor next time

[wxsatuser]

Practice makes perfect.

If there is patchy cloud I often mess about testing things out, it's time well spent.

Since early February there has only been one really good night here but I'm in for the long haul.

[brrttpaul]

I,ll be glad when I get hold of a power tank. At the moment I,m limited to my back garden which faces East and I have a tree and rooftops to contend with. I have been told to make one rather than buy one as the shop bought ones are not much use but making one is going to be a nightmare, to say I,m hopeless with electric is an understatement. I think I,ll go and get the Skywatcher powertank and be done with it.

[laser_jock99]

Both my 200 Ls have a nice action, not to tight or slack.

The Sigma is a bit tighter and holds focus for ever.

My Sigma 300mm F2.8 focus ring had a fair bit of backlash- hence my addition of the O-rings. But I have since found it improves the handling of other lenses.