Blurry views with high magnification

[RobinSturegren]

Hi! I'm completely new to this forum (and fairly new to stargazing as well), and I'm having a hard time using my 6.5mm eyepiece, as it always turns out way too blurry.

A little info; I live about 10km away from a fairly small city with a population of about 100.000, where I usually hang out on the golf course to get away from the light pollution. I use an Orion XT8 scope (focal length of 1200mm) with one 25mm Plössl and one of 6.5mm.

With my 25mm eyepiece I have absolutely no issues with blurry vision - I get sharp views of everything I observe. With my 6.5mm however, I can't get a good view of anything, at all. The moon (which I kinda assume is just way too close) looks really blurry, but as to Saturn, Jupiter, and Mars, same with the Orion nebula or star clusters. Is this normal? Perhaps the eyepiece gives me too high magnification? If so, maybe I should try a 10mm instead? According to their official website, however, the highest useful magnification for my scope should be x300, which I'm not even close to with this eyepiece. The eyepiece is unfortunately pretty cheap, the brand is called Bresser and it costed me about €50 from a Swedish astronomy shop (hence it probably being even cheaper in the US for instance). I figured my sky conditions probably is not the big issue, as the skies are very dark and the temperature being under the freezing point during the nights.

Any advice? Should I try spending a little bit more money on a 10mm eyepiece instead? Or which magnification would you suggest - I love searching for planets but I focus on deep-sky objects, trying to find a few nebulae etc. Thankful for any advice!

[alanjgreen]

Robin,

1200/6.5 = x184 mag

1200/25 = x48

Sounds like you are describing the effects of "too much" magnification either for the scope you are using or the atmospheric conditions or both!

The max useable magnification for a scope is said to be x50 per inch of aperture, so 8x50 = 400x

Therefore, your scope should take the 6.5 (x184) no problem, so maybe the eyepiece is not very good or faulty - can you borrow one from someone to try another and rule out the eyepiece as the issue...?

 

From UK, the atmosphere above limits us to x230 (or thereabouts), but we have had very poor seeing this week with the jet stream up above us (see link). You may get better results next time out

Or maybe your scope is not well collimated, have you tried a "star test" to view the "airy disk"?

 

Alan

 

[Putaendo Patrick]

Although a 200mm aperture telescope can in theory achieve much higher magnifications, in practice prevailing atmospheric conditions are the biggest limiting factor. Your 6.5mm EP will give you a magnification of about x185, which should be possible when the viewing is good - but not always. On many nights you may be limited to considerably less.

The Bresser 6.5mm is a economically priced Plossl design, certainly not a high end eyepiece. Even so, I would expect it to perform better - especially on the Moon. So I wonder if there might be a problem. As you move the focusing wheel, does it move into and out of focus?

I certainly would recommend another eyepiece in the 9 to 12mm range - but I'd try to find the problem with the 6.5mm first.

[John]

Hello and welcome to the forum

Your scope is a good one and the magnification given by the 6.5mm eyepiece should give dood results when the seeing conditions are steady but you may have been suffering from the conditions being discussed in this recent thread:

Perhaps try again on another night and see if things improve ?

 

[RobinSturegren]

 

13 minutes ago, alanjgreen said:

Robin,

1200/6.5 = x184 mag

1200/25 = x48

Sounds like you are describing the effects of "too much" magnification either for the scope you are using or the atmospheric conditions or both!

The max useable magnification for a scope is said to be x50 per inch of aperture, so 8x50 = 400x

Therefore, your scope should take the 6.5 (x184) no problem, so maybe the eyepiece is not very good or faulty - can you borrow one from someone to try another and rule out the eyepiece as the issue...?

 

From UK, the atmosphere above limits us to x230 (or thereabouts), but we have had very poor seeing this week with the jet stream up above us (see link). You may get better results next time out

Or maybe your scope is not well collimated, have you tried a "star test" to view the "airy disk"?

 

Alan

 

 

10 minutes ago, John said:

Hello and welcome to the forum

Your scope is a good one and the magnification given by the 6.5mm eyepiece should give dood results when the seeing conditions are steady but you may have been suffering from the conditions being discussed in this recent thread:

Perhaps try again on another night and see if things improve ?

 

Thanks for the replies!

I have checked the collimation using this collimation cap thingy that came with the scope, and it seems good. I have never heard of a "star test" though! Perhaps it's more accurate, if so maybe I should try it?
I've had the scope for two years (sadly I've been in France without it for the past 1.5 year, so I haven't had that much time with it), but I had the same problem back in 2015, and I haven't noticed that much of a difference in the past two months. Unfortunately I have no stargazing friends, and I haven't found any organisation or so nearby where I could ask for help, so asking for help online and buying new equipment is my only option.

[Ricochet]

Make sure you have allowed your scope to cool properly before trying high power viewing. If you have stored it indoors then I think the general guidelines are along the lines of 10 minutes per inch of aperture so at least 80 minutes. As others have said, the seeing was pretty bad here recently so you may have also experienced that. I regularly use a 7mm eyepiece with my 8 inch dob so a 6.5mm should be fine. 

[RobinSturegren]

20 minutes ago, Putaendo Patrick said:

Although a 200mm aperture telescope can in theory achieve much higher magnifications, in practice prevailing atmospheric conditions are the biggest limiting factor. Your 6.5mm EP will give you a magnification of about x185, which should be possible when the viewing is good - but not always. On many nights you may be limited to considerably less.

The Bresser 6.5mm is a economically priced Plossl design, certainly not a high end eyepiece. Even so, I would expect it to perform better - especially on the Moon. So I wonder if there might be a problem. As you move the focusing wheel, does it move into and out of focus?

I certainly would recommend another eyepiece in the 9 to 12mm range - but I'd try to find the problem with the 6.5mm first.

The moon looks absolutely stunning with my 25mm eyepiece, but with the 6.5mm I can't see that much detail, I kind of assumed it's because the moon is way too close for that magnification but perhaps that's not the case.

[RobinSturegren]

Just now, Ricochet said:

Make sure you have allowed your scope to cool properly before trying high power viewing. If you have stored it indoors then I think the general guidelines are along the lines of 10 minutes per inch of aperture so at least 80 minutes. As others have said, the seeing was pretty bad here recently so you may have also experienced that. I regularly use a 7mm eyepiece with my 8 inch dob so a 6.5mm should be fine. 

I'm usually out for at least an hour or two, and I always put my scope in the (not heated up) car at least an hour before I go out!

[John]

The Moon will benefit from high magnifications as will planets and double stars. While it is closer than the planets it is still 384,000 km away - plenty far enough to need some high magnification to see the finer details and smaller features.

My guess is that you have just found what a bad seeing night looks like rather than there being any problem with either the scope or the eyepiece.

 

[alanjgreen]

8 minutes ago, RobinSturegren said:

The moon looks absolutely stunning with my 25mm eyepiece, but with the 6.5mm I can't see that much detail, I kind of assumed it's because the moon is way too close for that magnification but perhaps that's not the case.

This is not the case. The moon will usually take "more" power as it is so big & bright. Its the brightness that allows for higher power. The more magnification you use causes the image to dim. As the moon is bright, it can take plenty of power (atmospheric conditions allowing)

 

[Putaendo Patrick]

Generally you should have no problem achieving higher magnifications on the Moon than on other targets. On a good night, I can often push magnification up to about x260 with a 120mm aperture refractor, and the detail is incredible.

[alanjgreen]

38 minutes ago, RobinSturegren said:

I have never heard of a "star test" though! Perhaps it's more accurate, if so maybe I should try it?

 

http://www.skyatnightmagazine.com/feature/how-guide/how-star-test-telescope

http://www.backyardastronomy.com/Backyard_Astronomy/Downloads_files/Appendix A-Testing.pdf  -try not to be distracted by the guys radiation sickness in the photo )

A collimation cap is designed to see if you have the secondary aligned with the focuser. This is part 1 of a 3 part collimation process. It cannot perform  stages 2 & 3 (at least for me!), for that you need a ....

 

Usually a "cheshire eyepiece" is used for stage 2-3 (and 1 as well)

https://www.firstlightoptics.com/other-collimation-tools/premium-cheshire-collimating-eyepiece.html

 

You also need astrobaby's collimation guide, here is a link...

https://stargazerslounge.com/applications/core/interface/file/attachment.php?id=241871

[LukeSkywatcher]

I cant think why a 6.5mm EP shouldnt work with a 200mm scope (especially in Sweden, a few miles outside of a small town). 50 euro for a Plossl isnt cheap either. Bresser certainly wouldnt be the top of the range brand, but certainly not bottom of the list either. I can only think that it is due to one of 2 things (or both):

1/ Local atmospheric conditions (on any given night).

2/ Eye relief of the 6.5mm eyepiece.

Many people (myself included) will use an 8mm eyepiece for observing planets or even the Moon. Ive found that anything below 8mm (i have a 200mm scope also), doesnt work too well on most nights,due to local atmospherics.

Is this the 6.5mm eyepiece you have?. I cant see any details about eye relief.

https://www.amazon.co.uk/Bresser-6-5mm-31-7mm-Eyepiece-SuperPlössl/dp/B004DZPBX4

 

[Louis D]

42 minutes ago, alanjgreen said:

A collimation cap is designed to see if you have the secondary aligned with the focuser. This is part 1 of a 3 part collimation process. It cannot perform  stages 2 & 3. for that you need a ....

 

Usually a "cheshire eyepiece" is used for stage 2-3 (and 1 as well)

I've never had any problems using my Aline cap to align my primary.  I just turn the primary collimation knobs until the black dot of the eye hole reflection is centered in the center spot ring.  It actually seems more accurate than using a laser.  I only use the laser to make sure the secondary is pointing directly at the center of the primary.  I use a cheshire tube to verify that the secondary is properly centered and rotated toward the focuser.  Maybe I've been doing this wrong all these years, and yet my defocused stars look nice and symmetrical.

[Louis D]

Defocus on a bright star and look at the resultant pattern.  Look on pages 14 and 15 of Astro Baby's collimation guide for illustrations of what to look for.  I'm going to guess you've got atmospheric turbulence and/or tube currents.  Basically, if you don't see a nice, steady, round bulls-eye pattern, you've got issues.  Turbulence is easy to see because the pattern constantly changes.  It reminds me of looking into a pot of boiling water.  Put your ungloved hand in front of the telescope.  You can actually see what looks like air boiling off your hand.

[alanjgreen]

5 minutes ago, Louis D said:

 Put your ungloved hand in front of the telescope.  You can actually see what looks like air boiling off your hand.

You had me worried there, thought you were going to say "put you ungloved hand in boiling water"

[Louis D]

1 minute ago, alanjgreen said:

You had me worried there, thought you were going to say "put you ungloved hand in boiling water"

Defocusing stars is something more people should try.  Not only can you see turbulence, you can see star colors easier and sometimes make out dim companions easier.

[rockystar]

I've got 6.5 mm EP and 200mm scope, and I can focus on the moon, even with bad atmosphere - I see the same as Louis D where it looks like the atmosphere is boiling, but the moon is still in focus behind it. Are you reaching the end of the focuser travel before you get to the focus point of the EP maybe?