vlaiv

1 hour ago, Lordspace said:

I have been trying for a few days now to get my newt (skywatcher 114p) collimated.

So far I get what looks like a perfect circle with a black circle inside when pointed at a star using back focus but if I out the same star out of focus using to much inward focus then donut center seems off.

What should I adjust if to much inward focus causes the inner circle to be off center??

 

Hopefully my question makes sense as I have no idea how to explain this stuff.

If you have different in/out star images (and you have your star centered in eyepiece) - in terms how they look collimation wise - it is your focuser that is bent.

Examine if focuser has any play in it and look how draw tube moves when you rack it in/out. Does it stay parallel the whole time?

Maybe tweaking the focuser could help fix that issue. Here is a nice guide how to try to sort it out:

http://www.astro-baby.com/Skywatcher Focuser Tune up/Skywatcher Focuser Tune-up.htm

Do you remember old cameras, like very old cameras?

They had accordion type shroud on them like this:

You could fashion some sort of shroud like that and have simple plastic ring on one side that you would put over your lens hood - that might be a piece of plastic canister or whatever. That way you can put light source (laptop + diffuser) some distance away from your mount and lens - maybe on a small table or even on a photo tripod (if you use tabled instead of laptop).

Although - you don' really need laptop - two pieces of diffuser glass + led strip glued to one will do the trick.

Dob mount is by far easiest mount to use for heavy scopes, it allows for seated observation (most scopes - depends again on size of the scope). It is very good mount type for visual and very cheap mount type.

There are a few drawbacks - no slow motion controls (but you can actually make them - DIY sort of thing). High power viewing with constant nudging can distract from viewing - there is however option to add EQ platform for tracking (up to 30 minutes and even an hour - but then it needs "rewinding"). You can motorize dob mount but that is not cheap thing to do.

It supports only newtonian type scope (it'll work for some other exotic types - like folded refractor and such - but mostly newtonian/newtonian based like MN and SN scopes) - most other types of scopes have eyepiece at the other end of the tube and that does not work on dob mount.

AltAz mount is very nice mount for visual - can be motorized, keeps eyepiece at the same position for most of the time, can be used while seated down. It has a "blind spot" - it is hard to track object at zenith, and with most scopes it is uncomfortable to view at zenith - eyepiece is at lowest position and requires bend neck to observe.

Principle of operation for these two mount types is basically the same, both are Alt Az mounts and tracking is the same.

EQ mount on the other hand is well suited for astrophotography. It is easier to track with both slow motion controls or with single motor that runs at constant rate (clockwork type motor), but newtonian scopes on EQ mount get eyepiece in weird positions.

It is a bit more time consuming to set up, as you need to do polar alignment, but if you want to have tracking for high power views - it is probably cheapest option (not goto but rather simple tracking motor - it can even be DIY).

Btw, AltAz mount and EQ mount are really different only in EQ wedge that is used to "tilt" mount head and do polar alignment. Some people used EQ mounts in AltAz configuration and some AltAz mounts work in EQ mode by adding polar wedge. There are even models that combine the two out of the box - like SW AZEQ5 and AZEQ6 models.

It really depends on what you want to use mount for and what scope do you plan on putting on it.

Those are quite artistic halos and I think they should not be removed from the image with any sort of processing.

17 minutes ago, Lordspace said:

I did crop the image but I don't have a raw sub on my phone. 

I had a scan over one of the subs on my camera and it looks like 99% of the stars have a trail so would that more likely be collimation than coma??

Coma and collimation of newtonian with parabolic primary are linked together.

Scope will always have coma, but if scope is collimated - that coma will have smallest impact on the image - center of the field will be coma free (coma will be too small to be noticed - it will be smaller than resolution of telescope) and as you move away from the optical axis - it will grow. It will be worst at the edges of the frame.

Here is diagram of the stars in the image with perfect collimation. Faster the scope - more coma it will show. 114mm aperture with 500mm FL is very fast newtonian and it will show a lot of coma.

Above is with perfect collimation - but if you have scope that is out of collimation - things will get even worse. First thing that you will notice is that those pin point stars are no longer at the center of the field - they will be to one side - very much like in your image above. One side of image will have much worse stars because of that. Stars will also be a bit more deformed than they would be from coma alone - there will be no sharp / pinpoint stars anywhere in the image.

If you think that you have poor polar alignment - that is easy to diagnose - stars in your image need to be streaking in same direction - all will suffer same type of distortion like this:

regardless where they are in the frame (corners or center of the frame - little streaks will be oriented in same direction).

Your image does not show that.

If you think you have field rotation - again, that is easy to diagnose, your stars should look like this:
 

There should be "center" of the frame - where stars are good, and then stars should be progressively longer streaks as you move away from that center. Also, direction of streaks should be perpendicular to line towards the center where stars are ok.

Again - that is not happening in your image.

Your image will suffer from coma (and it does suffer from coma) and you just need to make sure coma is "centered" - by properly collimating your scope if it is not collimated, and after using coma corrector to deal with remaining coma. That is probably not an option for you as there are no 1.25" coma correctors to be purchased.

10 minutes ago, Lordspace said:

It has been fully committed before I went out, everything looked spot on with the laser. Also it a skywatcher 114p but the mirror is about 2 inches further up the tube then normal.

Maybe above image is a crop? Do you have single unedited sub from your camera?

Coma is symmetric aberration - and it should be minimal in center of the image for well collimated telescope. It is not central in above image - if you take lines going thru the stars and their tail (coma tail) - they converge to roughly the same point in the image and it is not center of the image:

Either your scope needs to be collimated properly or you have cropped the image. In second case - it will help that you put target in the center of the FOV and then crop to it. Don't let it be to one side because it will lead to coma being asymmetric in the final image.

Of course, way around this is to use Coma corrector - that way you will get good definition across whole field, but like I mentioned - there is no coma corrector in 1.25" format commercially available. You can DIY one - do a search for 1.25" coma corrector and you will find instructions in ATM sections of astronomy forums for DIY 1.25" two element coma corrector - you can try that.

If you can't be bothered with that, maybe best thing to do is move to a bit larger but scope that is actually suited for AP - 130PDS. That one has 2" focuser and properly positioned mirrors so you can reach focus with camera.

I also vote coma. Scope needs collimation after mirror adjustment.

Unfortunately there is no Coma corrector in 1.25" format.

1 minute ago, Mr Spock said:

If people stop using a word to mean something different to it's original meaning there isn't an issue 

I sense we are getting there - could you say the word and original meaning (and why does it originally mean what it means )

What sort of light pollution do you have?

If you have stronger light pollution then you can actually use shorter exposures without loosing much in the end result. Only difference between short and long exposures for same total imaging time is in read noise, and only when read noise is significant component. You are using DSLR without cooling so you already have dark current noise that can be as much as read noise in short exposure. If you add light pollution noise to that, you could be able to achieve similar results with only 30s exposures.

It's certainly worth a try - just remember to do same total integration time and not same number of subs. If you imaged for example for one hour with 2 minute exposures and made 30 of them. If you go for 30s exposures - do one hour again and do 120 exposures.

Ok, I'm ultimately confused here.

I do understand that people use term - telescope "speed" to specify ratio of aperture to focal length and in that sense - there is only one understanding of the term "speed" or better call it F/ratio and it is in fact significant in many aspects of operation of telescope - for visual and for photography.

Only problem that I see with this is using term speed, faster, slower as that implies something that is simply not true, and in that sense yes, many people will confuse it with scope's ability to put photons on the sensor.

But if we agree that we don't call those terms - speed, faster and slower and instead use terms F/ratio, lower and higher, that don't have other significant meaning in this context - then I'm perfectly fine.

Are we on the same page here and we talk about F/ratio and related terms lower and higher and we are not discussing fast telescopes in terms of imaging speed (speed to reach certain SNR at given target resolution) but rather just discussing the fact that there are scopes which F/ratio is low in number - like F/5 and such scopes have certain properties and there are scopes that have F/ratio in for example 6-9 range and there are scopes that have F/15 - focal ratio. These scopes behave differently optically so yes, there is real distinction - just lets not call them fast and slow (I can't really think of reason to call F/5 scope fast - other than in photography context - what, fast to setup? Fast to show aberrations at low cost eyepiece? Fast as fast spending of money on more expensive eyepieces to get decent field )

@Mr Spock - what use of term speed did you have in mind?

I would say that we can divide factors into two distinct categories:

- ones that you can influence

- ones that you have no control over

Then concentrate on first group and understand what parameters are the best and how to obtain them.

54 minutes ago, Mr Spock said:

f7 is faster than f10. Don't confuse the speed of an optical system with it's ability to put photons on a sensor - that process was explained earlier in the thread. Speed has only one meaning - no need to be more specific than that.

I sort of agree with you, but given that it is called speed - a term that, as far as I know, originated from world of photography, and had meaning "speed at which image is formed on a film during image capture" - I think it would be good to point out that although we are talking about F/ratio and we use term "faster" instead of lower or higher - one ought not use it to compare speed at which image can be acquired with said telescopes.

2 minutes ago, alan potts said:

Thank you for that, yes I have seen 55mm quoted on reducers and flattener, simple mistake for the likes of me to make, must see if I have a T2 nose piece now, guess I still require the IR/UV filter?

Alan

Not necessarily. You can try without the IR/UV filter first and if there is bloat - then put filter in. Meniscus corrector should not produce much of secondary spectrum on its own - rest are mirrors.

Depending on the camera - you don't need T2 nose piece if you don't have one. My ASI models come with 2" nose piece - you can use that with 2" focuser - just insert camera with that attachment and it should fit focuser. Inner thread is T2 but outer diameter is 2" - same as 2" eyepieces.

2 hours ago, Cabstarman said:

Thanks for your input Mark, looks like you have a good little set up there. My reason for enquiring was for possibly getting the skymax 102 or 127 purely for lunar/planetary imaging. (I also have a short tube 80 for wide field stuff).

Do you feel the tripod to be adequately sturdy? Particularly with the pier extension in place?

I had my doubts about stability of that tripod, so I went for this instead :

That one is rock stable (I had HEQ5 class tripod leftover from upgrade to berlebach planet and I decided not to go for regular tripod sold with AzGTI).

If you plan to get AzGTI combo with Skymax 102 - be careful. I went for OTA + mount separately as version of Skymax that comes bundled with AzGTI seems to be different - it lacks back side collimation screws for example.

Yes, you can operate it both with laptop and smartphone.

There are a few ways of configuring it - it can create it's own access point and you can use smartphone or laptop to connect to it and then operate it or you can configure it to connect to already existing access point - and then you can use your device connected to same AP to operate the mount.

I'm not sure what the maximum distance is, but I suspect at least 10-20m with line of sight. I operated it at least 3-4 meters away via wifi connection.

There is no such thing as back focus for cameras - you probably think of adapters that you used to otherwise reach 55mm required by some field flatteners or coma correctors.

You don't need any of that for MN190 - just attach camera at prime focus with 2" to T2 nose piece and you are set to go. You should be able to reach focus like that - if not, you might need a bit of extension.

No need for any special distance since MN190 is corrected by meniscus disk at aperture.

11 hours ago, RustyShackleford said:

no, the first pic that you've labelled m48 measures 54mm. the second one that youve labelled t2 measures 48mm and the nikon adapter measures 42mm

 

Ok, I get it now

M54 is used for very large cameras and is one of "standard" threads.

Best thing to do is to get yourself M48 Nikon lens adapter like this one, provided it adds only 8.5mm of optical path:

https://www.rothervalleyoptics.co.uk/rother-valley-optics-m48-t-mount.html

But do check first with them if it has required optical path. If not, you can purchase ultra short Nikon adapter and then use M48 extension rings to get proper distance.

Or get this one:

https://www.teleskop-express.de/shop/product_info.php/language/en/info/p3629_TS-Optics-T-Ring-from-M48-to-NIKON-Bajonet.html

as it has proper optical length:

(btw what is show on image looks exactly the same as adapter at RVO so there is a good chance that one being 8.5mm also).

1 minute ago, saac said:

I bet if it did happen though it would be cloudy knowing our luck  

Jim 

But maybe it would still shine thru the clouds?

6 minutes ago, Damien1975 said:

Yes but don’t black holes suck matter in around them and grow? 

In fact - look at this recent discussion:

2 minutes ago, Damien1975 said:

Yes but don’t black holes suck matter in around them and grow? 

This is common misconception about black holes, that somehow same amount of matter (or even less) that was in star that produced black hole now suddenly starts attracting things more for some reason. It just does not happen.

Things that fall into black hole and get sucked into it - would definitively also fall into original star - difference being that star radius is many orders of magnitude larger than event horizon and you simply cannot come close enough to star center without colliding with the star first.

Once star is collapsed and all matter that was once star - gets into very small radius and has very large density - then funny stuff starts happening when you are close enough - but for things that are far enough - they just continue the same as before - when all that matter was still a star.

1 minute ago, RustyShackleford said:

Yeah, I just measured them with a ruler (I should have thought to do that sooner).

The outside of the thread on picture one is 48mm and the inside of the thread on picture two (the nikon adapter) is 42mm.

Ok, now I'm confused again - you attached two pictures - first one - showing what I believed to be M48 thread and unscrewed bit - this one:

and then this image - with that attachment screwed in place:

I was suggesting to try screwing that possible T2 thread (which is obviously smaller in diameter than M48) into your DSLR adapter and to see if it will screw in.

4 minutes ago, Damien1975 said:

It is only 600 to 800 lights years away isn’t that daily close if it becomes a black hole. The closest to earth is like 3000 light years, so this would become the closest to us 

mans i read we will know by February 21

Black hole that close will change nothing. If the closest star to us became a black hole - we could only tell that it went dark and nothing more.

Only real danger might come from gamma ray burst - if those are indeed produced by supernovas, and if it is directed towards us (not sure but I suspect GRBs emanate from poles of rotation of collapsing star - might be wrong at this).

3 minutes ago, RustyShackleford said:

ah right. No, it doesnt fit. the nikon adapter is too small.

Are you sure? Same adapter you used to attach your camera to 8" dob?.

I was probably not clear again sorry - let me try one more time - this time I won't try to explain it with words.

Try to screw this thread:

in here:

Both should be 42mm wide, and only reason can be thread pitch - it will start to screw in but will stop after a half a turn to a turn (if that happen don't force it, you can damage the thread).

20 minutes ago, RustyShackleford said:

Hi Vlaiv,

I tried as you suggested, removed the adapter and tried it against the nikon adapter but its too big. The outside diameter of the nikon adapter is just about the same size as the diameter of the threads on the reducer with the adapter removed.

I think I was not clear enough.

I meant that you try little thing that you removed not M48 thread. I was hoping you will figure out if smaller bit has T2 or M42 thread on it. If it has T2 thread - then it should fit without any issues.

Don't try field flattener on DSLR adapter - but rather than little thing that screws into field flattener.

Ah, ok.

From what I can see on FLO website for that FF/FR - it has M48 on both sides - scope side (2" filter thread is M48 - so you can connect it to scope via threaded connection if you focuser supports it - that is good to avoid tilt), and it has M48 on camera side - together with "M42 tread" which could be T2 thread actually rather than M42 thread.

From your image I see that adapter included - screwed in its place in second image. Check if that is indeed T2 thread - take it off and screw just it to T2/Nikon adapter that you already have. Be very gentle and don't force it - if thread has different pitch you should not be able to screw it in more than half a turn to a turn. If you can screw it in multiple turns and it screws in easily - then it is matching thread and it is in fact T2 adapter - then you should be all set.

At least I think so - you would be for Canon camera as it has lens mount that requires 55mm of distance and canon adapters are made like that - and it matches perfectly to distance required by this FF/FR.

As far as I can see  - Nikon F-mount has this distance at 46.5mm and if your adapter adds 8.5mm of optical path - you should be ok to exactly 55mm - unfortunately I can't see info on the link you provided, it does not say optical length of that adapter.