Is this in Focus?

[Marky1973]

Took advantage of the clear night last night to have a first go at M45. Took 30 45 second shots @ISO1600 after focussing with LIVEVIEW and then tweaked with the Bhatinov mask in place. The stars are round, but seem a bit fuzzy. Today's stupid question is whether people think this is in focus? Are the stars fuzzy like that as they are brighter than the others around it and the ISO was a bit high perhaps? I am pretty sure I was accurately focussed, but I am also paranoid.

The image is attached. Very little processing yet, just having a play and trying different things out so no colour as yet. And it is very grainy, lots of work to do!

[Kropster]

You have plenty of very small stars which suggests to me focus is ok..... and using the Bahtinov mask should get you spot on.

Bright stars do tend to flare and become bigger and there is a lot of nubulosity around the brightest stars making them seem even larger.

[Marky1973]

Cheers Cropster - now I just have to make it look nice! ;-)

[Marky1973]

Kropster even.....sheesh! :-)

[Carina Lass]

Blowiing up the medium stars shows a ghost of your spider and secondary.

I think your focus is not quite there

[Marky1973]

Hi Carina, looking again I can sort of see some artifacts like that (there ceratinly seems to be a dark line coming down from some of the larger stars), but this was taken through a refractor, so its not going to be the spider vanes - any ideas what this might be?

[Thalestris24]

Hi Marky

I'm never quite sure myself but I'd say your focus is pretty close. Any haze in the atmosphere can add noise and softness. I see, though, that your camera is suffering from the dreaded dark lines under bright stars which seems to be caused by the sensor:

http://stargazerslounge.com/topic/207337-vertical-lines-below-stars/

Louise

Edit: mine does that too

[Marky1973]

Thanks Louise. Not seen that before today, so will have to keep an eye out for it - sounds like it could be edited out to an extent (cloning?) And I did take BIAS/FLATS/DARK frames with the LIGHTS, so it obviously is a sensor issue. Not the end of the world as I am serving an apprenticeship at the moment, so will move on up to CCD at some point if I can learn the trade properly! ;-) It only seems to become more apparent after a bit of processing.....which is all I can do at the moment, as I have a lot to learn there as well - like getting a bit of colour into my pictures! I have the free trial of Star Tools to play with and the manual to work through!

[Thalestris24]

Thanks Louise. Not seen that before today, so will have to keep an eye out for it - sounds like it could be edited out to an extent (cloning?) And I did take BIAS/FLATS/DARK frames with the LIGHTS, so it obviously is a sensor issue. Not the end of the world as I am serving an apprenticeship at the moment, so will move on up to CCD at some point if I can learn the trade properly! ;-) It only seems to become more apparent after a bit of processing.....which is all I can do at the moment, as I have a lot to learn there as well - like getting a bit of colour into my pictures! I have the free trial of Star Tools to play with and the manual to work through!

Hi

It's only a problem with bright stars but I don't think you can process it out, unfortunately. Yeah, that's a very black and white image!

Louise

[Marky1973]

Yeah, I'm struggling with processing at the moment. Can do some basic stuff, but really need to spend some time with some manuals and tutorials.....although black and white IS more arty....isn't it? :-)

[glowingturnip]

Hi Marky

I'm never quite sure myself but I'd say your focus is pretty close. Any haze in the atmosphere can add noise and softness. I see, though, that your camera is suffering from the dreaded dark lines under bright stars which seems to be caused by the sensor:

http://stargazerslounge.com/topic/207337-vertical-lines-below-stars/

Louise

Edit: mine does that too

ugh, just read that thread you mentioned, and I have a new modded 1100d coming for Xmas, hope it's not affected. 

Not that I have any experience in it, but apparently the way to deal with blooming (and this looks like over-correction from blooming) is to shoot half the subs with the camera in a different orientation so that you can use the data from one set to patch up the bloomed data from the other set.

Juan recommended shooting at ISO1600 with the modded 1100d btw.

[Marky1973]

That sounds like it might just work Stuart! I was shooting at 1600ISO, so not sure if that does help, although my 1100d is unmodded, so you never know!

[Zakalwe]

The focus is well off....look at the dimmer stars and you can see that they are like doughnuts. A Bahtinov mask is a great investment. Don't forget to check during the night as the focus can drift.

There is a drift in the image too. Perhaps your polar alignment routine needs a tweak.

Keep at it though...its these final bits that are difficult to nail, but are essential.

[Thalestris24]

The focus is well off....look at the dimmer stars and you can see that they are like doughnuts. A Bahtinov mask is a great investment. Don't forget to check during the night as the focus can drift.

There is a drift in the image too. Perhaps your polar alignment routine needs a tweak.

Keep at it though...its these final bits that are difficult to nail, but are essential.

True... With my glasses on and a closer look

[Marky1973]

Thanks for the comments Zakalwe/Louise.....I have to say that is very frustrating to hear (although I need to hear it!) as I spent so long trying to get it right - initially in live view and then a final tweak using a Bhatinov mask so that the star burst was symmetrical - using the fine-tuning on the 2-speed focusser. I can see the need to make sure the alignment is right - really annoyed as I set it up the first time in the back garden and left it an hour while I had tea and Polaris was still nicely on the setting circle when I came back to it - but I had to move the rig to the front of the house, so it all moved and I didn't have as much time to set it up....so that would account for the drift....but the focus, I can't imagine how I could have got it closer -  focussed and locked - unless I knocked/moved it somehow.....so frustrating.....oh well, I'll have another go in January when we get another clear night!

Thanks for looking!

[glowingturnip]

are you using a laptop in the field ?  Using the laptop screen makes focussing a lot easier than on the camera LCD screen.  You can also use the Bahtinov focussing aid in APT, or alternatively Bahtinov Grabber to take the guesswork out of whether those bahtinov spikes line up properly or not - should give you very good focus.

[ollypenrice]

It's very hard to say, just by looking at the stars, whether or not they are in perfect focus. When we use Full WIdth Half Max to measure the diameter of a star at the mid range of its brightness (hence the name) no perceptible change can be seen in the stellar image even though moving the focuser slightly alters the readings considerably. For this reason I use FWHM but begin with a Bahtinov. The slightly grey appearance of the smallest stars suggests to me that focus is out. Even faint stars should look bright and point-like.

Stars aren't perfectly round but they are quite good. They have a slight bulge at about 7 or 8 o'clock. This could be guiding or perhaps slightly pinched optics.

If you capture with the PC and an astronomical camera control programme you could give FWHM a try. I like it.

Olly

[Marky1973]

Thanks Stuart - yeah used the laptop, but only with the bundled EOS software that came with the camera - so using live view on that - it isn't great, so perhaps I need to have a look at APT or something similar - I have read a bit about Backyard EOS, is that the same sort of thing?

[Marky1973]

Thanks Olly, will have a look at FWHM (or something similar) is discussed in Making Every Photon, so will go back and have a look at that again too. Perhaps it is time to upgrade from the free software....is it nearly Christmas?

[glowingturnip]

the demo version of APT which has most of the features, including Bahtinov focussing aid and FWHM focussing aid is free, and is only 13 euros for the full version.  Very similar to Backyard EOS, but that costs about 50 quid

http://www.ideiki.com/astro/Default.aspx

[Marky1973]

Yeah I did have quick look at APT and was pleasantly surprised by the price......there is a yearly license fee but that appears to be peanuts, so definitely worth it! Will have a look at the demo and try it out next time we have some clear skies.

[Carina Lass]

Do try it.

I think it is excellent and by paying the minimal fee, you get some really good extras.

[Marky1973]

Downloaded it last night and had a quick fiddle - will need to play properly with my camera, but the flexibility in just setting up imaging runs is an evolutionary leap over the bundle EOS software - looks like you can set it up to do all sorts of different length and ISO combinations in one imaging run, which will save a lot of time in itself. Will make sure I can figure it out and then will definitely be paying. I just need to find the "Cloud Dispersal" button......