Focus

[alan potts]

It is early days yet but I am struggling with focus, the focus seems to change, now whether this is focus slip or temperature change I am not sure.

I don't yet seem to have the hang of the tools in APT as the live view isn't actually live but a 2,3,or 4 second shot, or whatever.

Any tips from you guys as to the best way, I don't have one of those masks yet.

Alan

[glowingturnip]

you can make a mask for yourself with a craft knife and some stiff black card - generate the pattern here:

http://astrojargon.net/maskgen.aspx?AspxAutoDetectCookieSupport=1

and then use it with Bahtinov Grabber (http://www.njnoordhoek.com/?p=660).  I get critical focus every time in just a few minutes.

[alan potts]

2 hours ago, glowingturnip said:

you can make a mask for yourself with a craft knife and some stiff black card - generate the pattern here:

http://astrojargon.net/maskgen.aspx?AspxAutoDetectCookieSupport=1

and then use it with Bahtinov Grabber (http://www.njnoordhoek.com/?p=660).  I get critical focus every time in just a few minutes.

Stuart,

I have a delivery coming in the next couple of weeks from FLO, I have added a mask to the shopping list with all the other goodies. I was wondering if anyone had some good advice on the tools in APT.

Alan

[alan potts]

Another night wasted because of focus issues. Using APT and USB 2 makes focus very difficult, or the temperature drop is catching me out every other night. My biggest problem is I can't see anything to focus on. Last night I was playing doing a M13, an easy target, very poor result which looked fine when I focused on a nearby star. My IT mate is putting USB 3 into the laptop by way of a device that fits in the Express multi media socket. that I didn't even know was there. It may not have the voltage increase, I didn't ask him, but I hope it speed the camera up.

Alan

[Laurin Dave]

Alan

Have you tried it with the IR/UV cut filter..  that might be the problem... if you have then it clearly isn't

Dave

[Andyb90]

Have you tried the focus aid:

https://ideiki.com/astro/usersguide/focusing_aid.htm

Looks like it's similar to what I use in SGP. You get a number for the star size and need to get it as small as you can by adjusting the focuser.

[alan potts]

45 minutes ago, Laurin Dave said:

Alan

Have you tried it with the IR/UV cut filter..  that might be the problem... if you have then it clearly isn't

Dave

Dave, the cut filter is in, I just can't see a thing clear enough to get the job done. It seemed to behave different last night to the night when I took the data for the Pelican, which seems odd, nothing seemed clear on the screen, focus, or after sub was taken. This is why I didn't pick up the fault, learning process but I feel what you said the other day about USB 3 is the problem.

Alan

25 minutes ago, Andyb90 said:

Have you tried the focus aid:

https://ideiki.com/astro/usersguide/focusing_aid.htm

Looks like it's similar to what I use in SGP. You get a number for the star size and need to get it as small as you can by adjusting the focuser.

This is what I was using and though I had nailed it, it could be temperature drop, it goes from 20 or so down to 10 fairly quickly here. I feel the focuser is past it's best trouble is a new one is almost as much as another scope due to its size 118mm I think it is all replacements tend to be 90mm.

Alan

[Andyb90]

5 hours ago, alan potts said:

it could be temperature drop, it goes from 20 or so down to 10 fairly quickly here.

I find temperature changes make a significant difference. I refocus throughout the night. I did try auto focus, but couldn’t get it to work reliably. I may try again soon as I have a new focuser.

[Laurin Dave]

Alan

Same here, a 10deg temperature drop would put my Esprit 150 way out of focus.. maybe thats what is happening.. perhaps over the summer the temperature was more stable. Here its currently going from 17C to 4C overnight, a month ago it was 21C down to about 17C  

Dave

[alan potts]

5 hours ago, Laurin Dave said:

Alan

Same here, a 10deg temperature drop would put my Esprit 150 way out of focus.. maybe thats what is happening.. perhaps over the summer the temperature was more stable. Here its currently going from 17C to 4C overnight, a month ago it was 21C down to about 17C  

Dave

Dave,

I do have a weather system outside and in the house, rain, wind, temp etc, but I can't see this from the obsey. I feel the temperature of about a month ago would be about 28-30 at start of session falling to about 20 at dawn maybe even a bit higher. Whereas last night I would say it was 20 at start of session dropping to about 10 in 2 hours.

I paid a good deal of attention to it last night and it was a clear night with superb guiding (though one sub at start was another story). I refocused about 3/4 times but I didn't appear to get the focus I had at the start though the number suggested it was as good as it could be in APT using the focus aid.

The first sub I started running a good 10 minutes before as I was using PPEC in PHD2, I noticed the target ( wizard neb) was a bit off from where I would like so moved the scope. Then I restarted PHD using tools to select a star, guiding was terrible, all over the place, though the sub looked OK. Went back into PHD and manually selected a star and would you believe almost a straight line guide with figures of .35 second on RA and better on Dec. Just goes to show the program select a star is not always that clever. I am sort of beginning to wonder why I have just bought a new mount as this one seems to perform well in many parts of the sky. It is only really when below 20-25 degrees that the guide is a bit iffy.

Alan 

[alan potts]

Again last night I was very watchful about focus and failed awfully. Now I staked 32 x 4 minute subs into DSS and noticed something very odd after, these scores you get and other figures, start at 6900 plus (maybe good) and slowly drop away but not seriously so, 5900 then after 3 more subs down to 4500. However then a massive drop to 250. I wonder if I have dew forming somewhere in the system, be it on the front objective or on the sensor. I can recall seeing something like Anti Dew somewhere in the software programs but can't recall where, I wonder if this is my problem.

This is what I got the other night, no anything, and not very good guiding, 6x 4mins subs same settings as the next shot. No cooling, darks, flats etc and not much care taken either.

 

And this is what a few what looked decent subs gave from last night, cooled, darks flats etc etc, with very good guiding and a crystal clear night.

 

Just as much care taken, if not more, BTW 20 4 min subs were sdumped as it made this even worse. This is 12x 4 mins Minus 5, gain zero. 

Who ever said this was easy.

Alan

[alan potts]

Think I have solved my own problems, it is dewing up, the box was un-ticked int he APT settings program, kicked the cat as it has clearly been messing with the controls whilst I wasn't looking.

Don't know how this happened, must be more careful, here I didn't know I had un-ticked the box, now images are sharp and clear of the wizard nebula, cooling off very quickly again though so I will keep an eye on things,

A bit slow but great now I can type and send from the observatory, anyone want to talk me through how to set up Plate sloving.

Alan

[knobby]

From memory, it tells you what to download Alan ... Just download the platesolve 2 or ASPA ? And download the files for your scope / camera size