telescope sharpness problem? edges are really blurry looking

[JayTee]

I have the 80mm version of this and the glass is good enough for the price. Even though it has a slightly longer focal length, 40mm of extra focal length will not make that much difference in image size/FOV and it will slightly help with CA.

Cheers,
JT

[realflow100]

my issue is if its longer I will need to somehow extend the focusing mechanism further away. which i'm limited on. i'd need some kind of spacer or something for 40mm for the objective and i dont know what i would use to do that without it being floppy or flimsy/loose fitting

oh nevermind thats a whole entire telescope. that looks ok

the only thing that puts me off is the advertising of 300x power which is nonsense for a 70mm refractor. won't be usable at that kind of magnification unless the optics are absolutely perfect with a full apochromatic lens and perfect transparency and seeing conditions in a bortle 2 sky or better

Also it appears the mount is not a dovetail so I cant use it with my star tracker. its just some weird flat rectangular thing with 1/4 screw mount only. not very useful

[JayTee]

the only thing that puts me off is the advertising of 300x power which is nonsense for a 70mm refractor. won't be usable at that kind of magnification unless the optics are absolutely perfect with a full apochromatic lens and perfect transparency and seeing conditions in a Bortle 2 sky or better

Yeah, those of us in the "know", of which you are now one, realize that this is the hype that beginner systems are subject to. You also know that you can disregard this bogus info because you already know the "real" world capabilities of a shorter FL 70mm achromat. I believe that the scope I referenced will do all the things you want your current scope to do.

Cheers,
JT

[realflow100]

I will take a look at it and maybe check it out another time.
but I found a decent (below 200$) price for a 102mm refractor with an acceptable focal length that might be a better idea. cant go wrong with more aperture right?

[Lady Fraktor]

Nothing available there that matches 70mm diameter 360mm focal length. seems a better choice would be to just buy a better telescope at this point. or at least buy an optical tube assembly without a tripod since I dont need an extra tripod.

Keep an eye on Goodwill shops, local buy & sell and Craigslist, you would be surprised what turns up occasionally.
If you do see something post a link here so we can advise if it is actually worth it for what you are trying to do and if the price is good or not.

[realflow100]

I'm also not really able to "collimate" the objective in any way other than adding shims of tape
or aluminum foil with a tiny speck of elmers glue stick glue or something where i want them to stay.
theres no screws. the whole lens assembly retainer and everything just slots onto the end of the telescope tube push-fit on.
the only way I could really adjust it is tilting it a tiny bit somehow but that would be really hard to do and it would easily go out of alignment.
I tried rotating one of the lens elements around in a few degrees increments to see if I can cancel out the astigmatism somehow but it never seems to do anything. so I tried tilting the whole lens assembly various ways and havent had any luck either. Maybe a fraction of a percent barely visible difference. only thing that seems to change is chromatic abberation

There is a noticable color difference when focusing inward or outward. one way it makes yellowish things appear. and the focusing other way shows more neutral.

I was also thinking of doing the piece of glass thing in front of the focuser at an angle to try to compensate for the astigmatism (seems to only be in one direction for the most part) but I dont really have any good pieces of clear glass with good anti-reflection coatings to use.

[realflow100]

I tried doing 10 degree increments or so all the way around while rotating the lenses (unscrew slightly to give room and squeeze the plastic gently and flip to separate the lenses by a few millimeters so I can rotate the front lens separately from the rear lens) and it never really changed anything. Maybe very slightly a fraction of a percent.
I started by 90 degrees but it didnt make a difference either.

[realflow100]

I have discovered everything looks "doubled" in some direction or another. visible with 4mm eyepiece quite noticably especially on a bright light like a streetlight at a moderate distance away.
if i tilt the lens to the right a bit. it helps but it still looks doubled vertically for horizontal lines. and a bit sharper for vertical lines.. i tried slightly tilting it up and to the right but it doesnt get much better. its about 25% sharper but its hard to tell.

[realflow100]

ok It seems the diagonal is causing problems too. its crappy and causing some significant astigmatism on its own. without it the image is noticably sharper by about 75% but its still not quite perfect
so I need a better diagonal too. can anyone recommend me a cheap good one? preferably one with the widest opening and shortest so it's not causing any of its own vignetting?
i was thinking one of the prism types because they seem really short and have thicker glass in them which might be better than a standard mirror based diagonal and doesnt cost too much either

[realflow100]

My 100mm reflector telescope has a razor-sharp center and fine details easily visible even up to 200x magnification. with a barlow and 4mm eyepiece. (eyepiece is not even the best quality. showing clear signs of chromatic abberation)
but the eyepiece isnt the problem because the eyepiece isnt showing any issues besides some CA and the image still looks razor sharp at 100x and still very good and sharp at 200x (just darker image)
if I had a high quality eyepiece it'd be even sharper at 200x with no CA at all
so its still the refractor telescope having some weird issues with the lens and the diagonal

[Lady Fraktor]

Widest clear aperture and shortest lightpah would be with a prism diagonal but good ones are not cheap.
Your telescope will work fine with a mirror diagonal. For price vs quality the 1.25" GSO should do alright.
https://agenaastro.com/gso-1-25-90-deg- ... -ring.html

There are cheaper but no better quality than the one you currently have and should be avoided.

[realflow100]

what about this diagonal? it looks decent at least. and I really want the most posible clear aperture cause my current diagonal has a ton of vignetting and kidney-beaning/blackening
if i use the eyepiece by itself without a diagonal i have no problem putting my eye right up to the eye cup touching. and dont have to hover above the eyepiece (really uncomfortable to me) but its awkward to use like that

[Lady Fraktor]

Some eyepieces you are required to hover over this is called eye relief
I am not a fan of SvBony equipment, on the cheaper end of adequate.

The one I linked to above is the minimum I would recommend, also mirror diagonals tend to work better with short focal ratio telescopes.
When doing AP you do not use the diagonal anyways.

[realflow100]

yeah I know I just wanted a diagonal that would help with the vignetting issue somewhat and still have better quality. the diagonal included is horrible quality. i tried to wipe it off with a q-tip and it just smeared and ruined whatever coating was on there making it completely unusable

[realflow100]

i did another test just testing the effects of a 2x barlow. in order to get it to work I had to actually take the barlow lens itself off the end of the adapter. put it on another 1.25 tube and fit it into the barlow adapter itself and tighten the screw to hold it closer to the camera sensor. and on top of that I also had to have it not fully inserted into the end of the focuser in order to reach focus on stuff 100 feet away.
this is the result 100% crop on both images completely unedited.
its hard to tell if theres any difference in visible details between the two images. maybe a small percent. but turning the scope into a 720mm telescope doesnt seem to give me any advantage. and it also gives me a noticably darker image. by a few stops!

[John Baars]

I am not sure if the diagonal is completely unusable right now. It occurs to me that you just smeared a tiny spec of grease into a thin layer?? On a whole modern coatings are stronger than a Q tip and some alcohol can handle. Alcohol leaves a residu. Manufacturers know that their optical surfaces are cleansed every now and then.....

Once I asked a top-optician of the Royal Dutch Navy. He is an amateur too, but his daily work consists of cleaning, collimating, grinding, polishing and coating optics. Large optics. " How do you clean the expensive optical, by sea-salt attacked, equipment? ". He smiled at me and answered: "with nice soapy demineralised water and some kitchen-paper" ( !!! ) "Then rinse it with a wet kitchenpaper and if necessary dry off with a clean and soft scratchfree cloth."
"What about scratching the coatings?", I asked. He smiled again and replied: "If you want you can add diamond-dust to the paper for some serious scratching. Amateurs are too anxious and shaky about their precious coatings."

Since, I clean my optics that way. If you want you can use ordinary water too. Not a scratch, but fully cleansed optics. No residu either if dried with a cloth.
Since you think your diagonal is already "lost" at least you can have a try.

Another problem is the flatness of the used mirror. An ordinary mirror doubles his own aberration of the light it bounces back. I.e a perfect wavefront that hits a 1/10 wave mirror is bounced back as 1/5 wave. On a diagonal as 1/7 wave. There are many diagonals out there that can't meet the 1/4 wave to begin with. Many manufacturers dare to publish the accuracy of their diagonals. Problem is it was measured before the 64 layer coatings were applied. So be sure to buy a good one, as stated above. Consider your telescope as a chain of optics. It is as strong as its weakest point.

[realflow100]

Theres definitely scratches that wont come out for sure. its useless. some kind of hard grit got on it and its got a bunch of skinny easily visible scratches on it. and its too warped and not flat enough to use either. makes the image very blurry at any kind of high magnification.

[John Baars]

If it is scratched it will show as a misty image. If it is really warped too don't use it any more, it will cause severe astigmatism and other serious flaws.
A two times barlow makes the image four times larger. That are 2.02 stops. Correct. That's just physics and we can't do anything about it. But sometimes a good barlow makes the image large enough to observe certain details ( on the Moon for instance) with more comfort. It won't show more details if the telescope was already near its resolving limit.
At 0.5XD magnification roughly 80% of the telescope's resolving power is attained. At 1.0XD magnification 95%. (source: Rutten, Venrooij, Telescope optics,18.10)

[realflow100]

the diagonal was already showing bad astigmatism on higher magnifications. making the image extra soft and blurry (weird doubled look to high contrast edges at higher magnifications)

my camera is 15mp and a 100% crop shows approximately the magnification that I would see visually at about 70x to 90x magnification
adding a barlow reveals just a bit more detail than without. but the image is dramatically darker. so I dont think I get enough benefit of using more magnification at all. it'd be much better if I just had a bigger telescope with a longer focal length

I really have my eye on a 102mm meade refractor telescope. would be really nice to have the higher quality. more aperture. and MASSIVELY BETTER focuser (looks to be capable of directly attaching to camera without a 1.25 adapter) so no chance of vignetting and much more light gathering ability.
but the price went up so i'll need to wait for a sale or something.

[realflow100]

When focusing my telescope with my camera should I have to lower the exposure enough that the star is just barely visible with 10x digital zoom so I can focus it to a point?
its impossible to focus perfectly if I have the exposure set higher where the star is a big white circle instead of a small point
if its a colored star like betelgeuse or arcturus it becomes big and pure white and so its hard to tell when its really focused properly

however if I do get it focused perfectly. and my telescope tracker is aligned well. I can get reasonably fine and sharp looking stars. but there is noticable chromatic abberation on any semi-bright stars