The EQ3 DSO Challenge

[Stub Mandrel]

2 minutes ago, bobro said:

The camera is set to ISO800 as I understand 400/800 helps to keep noise lower.  It looks like longer exposure with my setup is still required.

I use 800 now, seems to give the best results.

[bobro]

9 minutes ago, Nigel G said:

I think you might pick up more detail if you centre the Southern half rather than centre the complete nebula. I loose detail around the edge with my reflector so try to get the most detailed parts in the middle of the frame. Maybe mosaic 2 images, but still well done.

Thanks Nige, I'm sure you are correct in that the southern part could provide more interesting imaging. A mosaic?  That means I have to find it again - with accuracy of the area being imaged - aaarrrrghhh! I better get a goto upgrade! 

[Art Gecko]

8 minutes ago, bobro said:

The camera is set to ISO800 as I understand 400/800 helps to keep noise lower.  It looks like longer exposure with my setup is still required.

How far does that push the histogram spikes to the right? I do agree with keep the ISO as low as possible to help the SNR, but as I'm not getting the length of exposures you guys are getting, I have to push the ISO up to get a clear gap between the left hand edge and the start of the spike... If you're both using around 800 I might have to bump it up as high as 6400 to gather that light!

[bobro]

ISO setting may not do what you think (excuse me if you already understand this). The camera captures photons irrespective of the ISO setting. What the ISO setting does is enable amplification when the sensor is read. That is why a balance between the read noise and ISO setting is relevant - you want to keep read noise in the image as low as possible.

So why not set the ISO to maximum? Well, to ensure bright parts of the image (stars) do not saturate and to leave room for stretching in software.

So setting a high ISO value on a camera isn't necessarily a good thing - if I understand correctly (as always...).

I understand you are going for high ISO as the exposures are short. That can help balance out read noise in faint detail, but won't help with the rest of the image.

[Stub Mandrel]

Clear gap at teh left doesn't mean anything much - it only provides a space for signal values of pixels that are darker than the background sky - ok if you are after the IFN or dark nebulas.

[Art Gecko]

7 minutes ago, bobro said:

ISO setting may not do what you think (excuse me if you already understand this). The camera captures photons irrespective of the ISO setting. What the ISO setting does is enable amplification when the sensor is read. That is why a balance between the read noise and ISO setting is relevant - you want to keep read noise in the image as low as possible.

So why not set the ISO to maximum? Well, to ensure bright parts of the image (stars) do not saturate and to leave room for stretching in software.

So setting a high ISO value on a camera isn't necessarily a good thing - if I understand correctly (as always...).

I understand you are going for high ISO as the exposures are short. That can help balance out read noise in faint detail, but won't help with the rest of the image.

I wasn't totally unfamiliar with the ISO settings, but I do admit I haven't been using a DSLR long andthat was well explained! Nice one!... I don't normally push my ISO up that high either... well I do for test shots, but then lower the ISO and find a nice balance between that and the exposure length.....

3 minutes ago, Stub Mandrel said:

Clear gap at teh left doesn't mean anything much - it only provides a space for signal values of pixels that are darker than the background sky - ok if you are after the IFN or dark nebulas.

..... to get a base line for my background, as Neil has explained.... It is my personal choice to do this I guess, but I feel its a good idea to have a base value for the background sky.... As I've said before and will no doubt say again, I may be wrong in what I'm doing but it's a learning curve and I'm still very much at the bottom of it!! So I'm quite happy for all the pointers, thanks guys!

[mikey2000]

Did you ever see this page?  What ISO is best for my DSLR and astrophotography?

lots of theoretical stuff and some handy charts to help pick the correct ISO for various camera models.

[Art Gecko]

7 hours ago, mikey2000 said:

Did you ever see this page?  What ISO is best for my DSLR and astrophotography?

lots of theoretical stuff and some handy charts to help pick the correct ISO for various camera models.

Thanks Mike, yeah, I have read that page before, it is a very informative write up!

Art

[Stub Mandrel]

7 hours ago, mikey2000 said:

Did you ever see this page?  What ISO is best for my DSLR and astrophotography?

lots of theoretical stuff and some handy charts to help pick the correct ISO for various camera models.

There's a chunk in the middle of that page telling me the best for my camera is ISO9001

[Art Gecko]

Well, my attempt last night was just an epic fail! I've never shot Nebulae before (except the obligatory M42 on my iPhone) so I spent about 2 hours imaging... only used about 40mins of subs... and processed to find I'd been off target all along!!... So you might find me behind Bob in the queue for a Goto!

I did get a tiny bit of nebulosity... but not enough to identify any particular part of the nebula to see how far out I was.... Bare in mind I'm using a stock camera (unmodded) so I'm only gathering 20-30% of the Ha wavelength... so it's quite dim even though I've stretched it beyond a ridiculous amount!

Maybe I should stick to Galaxies...

[bobro]

Art, are you aware that you can submit an image to nova.astrometry.net to identify where in the sky the image is?

As I image from my back garden and have Internet access on my laptop, I take a quick snapshot and upload it as part of finding the target. You almost had the Pelican Nebula!

[Art Gecko]

4 minutes ago, bobro said:

Art, are you aware that you can submit an image to nova.astrometry.net to identify where in the sky the image is?

No I was not aware of that! Thanks Bob!..... Hmmm I'm not sure it'd help me in quite the same way though, as I shoot untethered as well, so I can't really do that until I've detached my camera at the end of the session..... Unless I buy the dongle to send the pictures to my phone, that might work.

I got completely the wrong nebula then haha... Thanks for identifying it though!

[Stub Mandrel]

Creditable to get ANY of the pelican with an unmodded DSLR. If you can hit the NAN (it is easy to miss!) it is much brighter.

[bobro]

Well if I can't find the target with the scope - put a wide angle lens on!   21 subs @ 120 secs with 135mm lens. Unfortunately didn't notice the camera display was on - some light from this registered on the sensor. It did show me how much brighter the image is with the lens at f4 when compared to my scope, so I think I'll do a comparative test to find out the real f# of the scope.

Edited June 2, 2017 by bobro

[Alien 13]

15 hours ago, mikey2000 said:

Did you ever see this page?  What ISO is best for my DSLR and astrophotography?

lots of theoretical stuff and some handy charts to help pick the correct ISO for various camera models.

Strange results according to the table my camera is ISO less like a Nikon...

Alan

[mikey2000]

From last night....   I fear my efforts were hampered by a half moon and this pesky summer sky that never really gets dark.

 

This is IC342.  It's a fairly large galaxy but it's faint (obscured by milky way dust) and it was quite low in the sky.  So, I had to stre--------tch this one quite a lot then bash it around in photoshop

16x3mins and 8x2 mins

 

 

I started watching the files coming in on DSSLive and realised there was almost nothing there, so for the last few minutes of the night, I switched to the Sombrero....

 

 

 

[mikey2000]

And then I clicked 'submit' by accided :-)

 

Here's the Sombrero M104, now with a grand total of 24 mins..  Then I went to bed.

[Art Gecko]

2 hours ago, bobro said:

Well if I can't find the target with the scope - put a wide angle lens on!   21 subs @ 120 secs with 135mm lens. Unfortunately didn't notice the camera display was on - some light from this registered on the sensor. It did show me how much brighter the image is with the lens at f4 when compared to my scope, so I think I'll do a comparative test to find out the real f# of the scope.

Looking at your picture, I think I can see where I went wrong with my star hopping from Deneb... and NAN does look a lot brighter than pelican!

Interested in how you've altered the focal ratio of your scope Bob?

@mikey2000 those are two fantastic pictures!

[bobro]

33 minutes ago, Art Gecko said:

Interested in how you've altered the focal ratio of your scope Bob?

Replaced the scope by a camera lens (£18 from ebay). Note - the can is full of sand - contents weren't wasted! 

[Art Gecko]

10 minutes ago, bobro said:

Replaced the scope by a camera lens (£18 from ebay). Note - the can is full of sand - contents weren't wasted! 

That is an impressive display of DIY skills!!!

It's not quite what I meant though... You said you need to test to find the f# of your scope, but how has it changed from when you bought it?

[bobro]

24 minutes ago, Art Gecko said:

You said you need to test to find the f# of your scope, but how has it changed from when you bought it?

A few things :

• Although the scope is nominally f5, it isn't really as the secondary mirror blocks some light (bought this way of course)
• 40mm was cut from the OTA to make it focus with a DSLR, likely resulting in some light loss at the secondary and also some loss up the focuser tube as the camera sensor is far up the tube
• The (DIY) coma corrector results in additional vignetting and some light loss

[Art Gecko]

19 minutes ago, bobro said:

A few things :

• Although the scope is nominally f5, it isn't really as the secondary mirror blocks some light (bought this way of course)
• 40mm was cut from the OTA to make it focus with a DSLR, likely resulting in some light loss at the secondary and also some loss up the focuser tube as the camera sensor is far up the tube
• The (DIY) coma corrector results in additional vignetting and some light loss

Ah, I see, so the mirror is still f5, but you want to measure the amount of light loss from the modifications.. Fair enough, that makes good sense!

[Peco4321]

M92 last night:

Skywatcher 150p on eq3-2 with enhanced motors, Canon 1100d at prime focus, Stack of 60 x 10 sec ISO 1600 in DSS, Master offset Bias frame, No darks or flats, stretched in GIMP a little

 

Seeing was nice even though there was a very bright moon 3rd June

[bobro]

As previously mentioned, I wondered what was the actual f# of my scope, what with the obstruction due to the secondary mirror, scope shortening to achieve focus and the addition of a coma corrector. Here are the results of using the camera with a 135mm lens at f# from 5.6 to 16, comparing with the camera on the scope at a nominal 5. Same exposure time and ISO for all images.

Edited June 5, 2017 by bobro

[Nigel G]

11 hours ago, bobro said:

As previously mentioned, I wondered what was the actual f# of my scope, what with the obstruction due to the secondary mirror, scope shortening to achieve focus and the addition of a coma corrector. Here are the results of using the camera with a 135mm lens at f# from 5.6 to 16, comparing with the camera on the scope at a nominal 5. Same exposure time and ISO for all images.

 

Very interesting an very noticeable difference, when I use my 135mm lens at F3.2 I gather a fair bit more light than my 150p f5 reflector which surprised me .

These are same modified camera same exposures both with CLS filter, the 135mm has been heavily cropped for this post but there is far more dust visible in the 135mm image.

Nige.