300mm lens

[brrttpaul]

Hi I have the HEQ5 mount and a skywatcher 150, but I was thinking rather than attach the camera to the scope could I just put the camera directly on the mount? I would have thought so. I have a 300mm 2.8 prime lens but I also got a 2x converter which will take it to a 5.6.  Seeing as I,m still learning and finding my way about what would be a good starting point for subs, seconds etc. I was thinking of doing 60 sec subs ISO about 800?

[ollypenrice]

You can take great images with a prime lens on a tracking mount. If you bump up the focal length to 600mm you'll need to be tracking very well and, realisitically, autoguiding for longish subs. Personally I wouldn't start that way, I'd stick to 300mm and enjoy the ability to expose for longer.

It is very hard for lenses to give clean stars to the edge when wide open even when, on terrestrial targets, images look sharp across the chip. Stars are hard for optics to handle. If you want to avoid diff artefacts from the diaphragm you could make a front aperture mask.

Another top tip from Psychobilly is to focus carefully on a star that lies on an intersection of the 1/3 lines. (Imaginary lines parallel with each side of the chip but a third of the way over to the opposite side. This will give you the best focus compromise across the whole chip and is remarkably effective.

Olly

[Alien 13]

What Olly said, camera lenses in the 200-300mm fl range are great for capturing nice widefield images with quite a bit of detail too.

Alan

[wxsatuser]

This is the way I do most of my imaging using two lenses and one tiny Borg scope.

Normally run the Sigma at f/4, Canon EF200mm L goes wide open at f/2.8 and the Borg is f/3.8.

With guiding and an LP clip filter I do subs of 5minutes easy and on good nights it can get to 10minutes.

Here is my 60Da and Sigma 105mm with guiding gear.

[LukeSkywatcher]

I used to enjoy a bit of very very casual wide field photography using my 18-55mm and 75-300mm Canon lens on my 8115 tripod but i gave up because of 2 reasons:

1/ I was told/read to focus the camera to infinity. I dont know where the focus point of infinity is on my camera. There is no marking on the camera or lens that denotes infinity.

2/ Stars just were never bright enough to see on the display to be seen and as such focusing was impossible. I could use the 10x zoom function to get a star in view and focus that way, but wouldnt that just give me an image of a single star. If i zoomed back out, would the camera still be focused but give a wider view.

Ive just never felt the pull of the dark side. I'm very happy to leave it up to the pros and amateurs and enjoy the amazing images. I'm not just talking about astro images either. 

[wxsatuser]

2/ Stars just were never bright enough to see on the display to be seen and as such focusing was impossible. I could use the 10x zoom function to get a star in view and focus that way, but wouldnt that just give me an image of a single star. If i zoomed back out, would the camera still be focused but give a wider view.

Not with 10x Liveview........this does'nt alter focus.

My method is to aim at a bright star and use 10x Liveview to focus.

I look for the different coloured rings of inside and outside focus.

Then I find the centre between inside and outside focus.

The colour should be a single colour, normally a yellow white colour.

[Knight of Clear Skies]

Good advice in the posts above. Unguided, the best I've been able to manage is 120 second subs at 200mm. There are plenty of large targets up there suitable for this focal length, for example here's the Pleiades at 200mm/f5.6.

The image above shows why a front aperture mask might be a good idea. I sometimes like spiky stars or am at least indifferent to them but in this case the diffraction pattern is hiding some of the nice detail in the reflection nebulosity.

Focussing can be very tricky with slow lenses but at f2.8 is shouldn't be too much of a problem. I usually open the lens right up and boost the ISO level for focussing on liveview at maximum magnification.

[LukeSkywatcher]

Not with 10x Liveview........this does'nt alter focus.

My method is to aim at a bright star and use 10x Liveview to focus.

I look for the different coloured rings of inside and outside focus.

Then I find the centre between inside and outside focus.

The colour should be a single colour, normally a yellow white colour.

So to focus i can use 10x zoom on the camera display and then back out for a wider image and the camera will remain focused?.

I am not using a laptop in any of this..........just so you know. Its simply tripod/camera/lens.

Cheers.

[brrttpaul]

I think so  the zooming in on live view dosnt alter where it was originally, least I dont think it does. The clouds are clearing nicely I may give this a go later, my biggest problem is from the garden my viewing is very limited mainly east. Im not expecting much but the practise now will make it all the more easier when the darker nights come. I noticed last night when I set up it only took me 15 mins to polar align and have everything up and running, last week it took me over an hour, cant believe I was so stupid with the polar aligning looking at it now

[Knight of Clear Skies]

So to focus i can use 10x zoom on the camera display and then back out for a wider image and the camera will remain focused?.

I am not using a laptop in any of this..........just so you know. Its simply tripod/camera/lens.

Cheers.

Yes, that's right, changing the liveview zoom won't affect the focus. You need to click the lens into manual focus mode for astrophotography.

Im not expecting much but the practise now will make it all the more easier when the darker nights come. I noticed last night when I set up it only took me 15 mins to polar align and have everything up and running, last week it took me over an hour, cant believe I was so stupid with the polar aligning looking at it now

I find that with many aspects of astrophotography. It's not that a lot of it is difficult so much as a learning curve, and it takes me a bit of repetition to get my head around things.

[wxsatuser]

So to focus i can use 10x zoom on the camera display and then back out for a wider image and the camera will remain focused?.

I am not using a laptop in any of this..........just so you know. Its simply tripod/camera/lens.

Cheers.

As the other posts, yes.

As Knight states, manual focus, you don't want auto on.

Liveview does'nt alter focus, all it's doing is zooming the image from the sensor.

Your only limitation with the tripod is length of exposure but you can still get some nice wide shots.

I don't tether my 60Da, I just use an intervalometer to control it.

[Thalestris24]

Hi

Just a warning about liveview - it rapidly heats up the sensor, so try to minimise time spent in liveview and allow some time to cool before actual imaging.

Louise

[LukeSkywatcher]

As the other posts, yes.

As Knight states, manual focus, you don't want auto on.

Liveview does'nt alter focus, all it's doing is zooming the image from the sensor.

Your only limitation with the tripod is length of exposure but you can still get some nice wide shots.

I don't tether my 60Da, I just use an intervalometer to control it.

Always manual focus for me. Live view (10x zoom) doesnt alter focus...............good to know. Yes, fixed tripod does mean short exposures, but many shorts can be stacked to give pleasing results.

Great stuff people. I have never really used my 300mm lens. I'm now inspired to give it a go.

Cheers

Paul.

[LukeSkywatcher]

Hi

Just a warning about liveview - it rapidly heats up the sensor, so try to minimise time spent in liveview and allow some time to cool before actual imaging.

Louise

I'd never have thought that a bog standard Canon 450D needs a cooling down period like some scopes. 

Good to know this. How long would you suggest?. I'm assuming the cool down period involves leaving the lens on the camera, so moisture etc doesnt get to the sensor.

[Earl]

I'd never have thought that a bog standard Canon 450D needs a cooling down period like some scopes. 

Good to know this. How long would you suggest?. I'm assuming the cool down period involves leaving the lens on the camera, so moisture etc doesnt get to the sensor.

its the effect of the chip heating up while in live view that is more the problem, once you hve foucs, leave it for 10 mins before you star imaging i guess.

I never did like focusing a dslr, im not a fan of touching a device to get focus at all really and prefer to do it remote... which i think you can do in eos utils?

[Thalestris24]

I'd never have thought that a bog standard Canon 450D needs a cooling down period like some scopes. 

Good to know this. How long would you suggest?. I'm assuming the cool down period involves leaving the lens on the camera, so moisture etc doesnt get to the sensor.

Hi

It's not the same kind of cool down. Whereas ccd astro cameras have integrated TEC cooling, standard dslrs do not. So using liveview, and even normal long exposures, generate a lot of heat which gives rise to thermal noise which in turn degrades the image. I can't give a time to wait after using liveview. Maybe 10 mins depending on ambient temperature and how long you've had it in liveview mode. You'll get a feel for it with experience

Louise

[Earl]

Does apt have a temp sense readout built in? somethign ratles around my skull about it. or does it depend on the chip?

[LukeSkywatcher]

Hi

It's not the same kind of cool down. Whereas ccd astro cameras have integrated TEC cooling, standard dslrs do not. So using liveview, and even normal long exposures, generate a lot of heat which gives rise to thermal noise which in turn degrades the image. I can't give a time to wait after using liveview. Maybe 10 mins depending on ambient temperature and how long you've had it in liveview mode. You'll get a feel for it with experience

Louise

This is good to know. It took me a while to find an balance between ISO and exposure time in my last house due to LP. I know i can get longer exposures in the new house......never considered letting the DSLR cool down. 

[Alien 13]

When I started I found that using liveview to focus then seting up the internal 10 shot sequence timer that puts an initial 10s delay before shooting was enough to cool the sensor, the timer is limited to 30s max per sub but thats plenty on a fixed tripod.

The whole process looks cool when operating with the timer leds flashing on countdown.

Alan

[Knight of Clear Skies]

Personally, I wouldn't worry about letting the sensor cool down after using live view, 10 minutes is a lot of valuable imaging time to discard. Yes, there may be a little more thermal noise in the subs but stacking (especially kappa-sigma) is very good at removing this. I also don't give the sensor more than about 15 seconds to cool between subs for the same reason. It's all a bit of a trade off.

I do turn off the camera display while taking subs as this can generate a lot of heat.

[Earl]

the batery can also get warm, if you can use a mains psu unit for it that an save on heat, best thing to do is do a run withut taking cooling into consideration then one with and deciding when you have the results to compare.

[wxsatuser]

I don't let the sensor cool during imaging, just a short gap for the card write.

As to Liveview.

Basically I know the focus position of each lens and just tweek it each imaging session.

It takes barely a minute just to get it right, it keeps Liveview to a minimum.

[Thalestris24]

Personally, I wouldn't worry about letting the sensor cool down after using live view, 10 minutes is a lot of valuable imaging time to discard. Yes, there may be a little more thermal noise in the subs but stacking (especially kappa-sigma) is very good at removing this. I also don't give the sensor more than about 15 seconds to cool between subs for the same reason. It's all a bit of a trade off.

I do turn off the camera display while taking subs as this can generate a lot of heat.

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

[brrttpaul]

Now I wonder if that is what went wrong with mine last night, I switched liveview on and left it on while taking subs, anyway the results were rubbish and binned them scratching my head didnt even occur to me about the heat.. I, think I will give it a go tonight and probably end up pointing it towards the pinwheel galaxy as its high above me I cant stay out late so it will just be a sort of trial run. I will prob try 3min subs x 10 at iso 1000 see how it goes

[Earl]

I think it depends on the camera they all behave differntly and have improved over time with heat control, as any heat in electronics unless intended is not ideal.