Help with

[Rose]

Hi all

I've only posted here once before to ask for advice on which telescope to buy. At the end of April I took delivery of a Skywatcher 150 Dob. I have been making slow progress partly due to the weather and short nights of summer but have been getting out a bit more recently.

Last week I ordered a new eyepiece, the BST explorer 15mm and was using this last night to look at the moon. I can definitely see an improvement on the stock eyepieces which I am happy with.

However when I barlowed (x2) the lens to look at the moon, I noticed that my eyelashes (or rather the shadow of my eyelashes) seemed to be getting in the way, and I think I could see the secondary mirror in the middle of the image? Can anyone explain this...the magnification I was at would have been x160 which I wouldn't have thought was too high for my telescope? Is this to do with the eye relief or something else? Have I chosen the wrong EP for my scope?

Any help/guidance would be much appreciated.

Many thanks

Rose

[JamesF]

If you put the barlow in you will almost certainly need to refocus. If you're too far out of focus you'd often expect to see the image of the secondary mirror. It can also happen if your eye is too far from the eyepiece, but that doesn't sound like it's the case in this instance.

James

[Rose]

Thanks for your input.

I'm quite surprised you suggest its the focus as I did adjust slightly once the Barlow was in, and it appeared to be ok although perhaps not as good as it could have been so I will try again this evening, thanks very much. I think maybe I assumed it was the seeing rather than the focus meaning the moon wasn't sharp, so didn't spend as much time focussing as I should.

Rose

[JamesF]

It's my best guess for the moment. When a newtonian scope is a long way out of focus you tend to see an image that looks like a white ring with a black disc in the middle. As you get closer to focus it will shrink and form a proper image.

James

[Stu]

It does sound like focus to me. Putting a barlow in normally requires a significant refocus, not just a slight adjustment.

Looking at a bright star rather than the moon will make it far more obvious if it is focus or something else.

Good luck

Stu

[Rose]

Thanks both, forecast looks good for tonight so will hopefully experiment later.

If it is just the focus then thats good because its easily sorted! I am slightly rolling my eyes at myself though!

[DirkSteele]

Agree with BigMakStutov, introducing a barlow in to the system will usually require a decent amount of refocusing. The only barlows I can think of that are essentially parfocal are the Televue Powermates.

[stevetynant]

I know you've probably covered this but the eye piece in the BSTs screws upwards away from the lens -you have screwed it outwards haven't you? You'd be suprized that some people didn't know this months after using the lens.

[Rose]

I know you've probably covered this but the eye piece in the BSTs screws upwards away from the lens -you have screwed it outwards haven't you? You'd be suprized that some people didn't know this months after using the lens.

Thanks for your suggestion, yes, I screwed it out and the further out it came the better the eyelash problem seemed to get...which is what prompted me to ask if it was something to do with the eye relief.

[Spec-Chum]

I know you've probably covered this but the eye piece in the BSTs screws upwards away from the lens -you have screwed it outwards haven't you? You'd be suprized that some people didn't know this months after using the lens.

And some ep's don't hehe. I damn near broke my brand new sterling plossl by trying to unscrew the eyecover.

It was very stiff for a reason.

It's locked. Oops

[Rose]

Thanks everyone for your help.

I was out with my scope this morning and think that what I thought was the secondary mirror is actually a spec of dust in or on the lens. The eyepiece came with a cleaning cloth but I understand these things are better left alone? When looking at Jupiter there was quite a lot of reflection, sort of like a halo around the planet. Is this a limitation of the lens or does this happen with all bright objects?

[JamesF]

Sounds like the result of moisture in the air or dew on the optics I think. In my experience fuzzy halos around bright objects are an inevitable consequence of dew forming on the optics. That would definitely be the first thing I'd check if it happens again. Lots of SGL members have made cheap dew shields for their scopes from sections of camping mat though you can buy them. It's not a huge problem to do something about.

James

[Rose]

Sounds like the result of moisture in the air or dew on the optics I think. In my experience fuzzy halos around bright objects are an inevitable consequence of dew forming on the optics. That would definitely be the first thing I'd check if it happens again. Lots of SGL members have made cheap dew shields for their scopes from sections of camping mat though you can buy them. It's not a huge problem to do something about.

James

Thanks, didn't think of that.

I have got a dew shield for the scope but don't think there is a lot I can do about dew on the eyepiece (It seems to fog up very easily!) aside from the electric dew heater strips?

[JamesF]

I'm surprised a dob eyepiece fogs up easily. I tend to have most problems with eyepieces when they're out of the scope, so I usually keep them in my eyepiece case or in my pocket, with the caps on. I guess it's easy to breathe on them without realising and that can't help. Otherwise perhaps it's worth just putting the end cap back over the top of the eyepiece when you're not actually using it?

James

[rwilkey]

Hi Rose, a little late in the day, but anyway. I think it's just a case of getting used to using the optics, you are not doing anything wrong, it's just learning to see through a different medium and getting used to it. Already over a little time you will have found viewing getting easier I am sure. Anyway, good luck and enjoy the views.

[Rose]

Hi Rose, a little late in the day, but anyway. I think it's just a case of getting used to using the optics, you are not doing anything wrong, it's just learning to see through a different medium and getting used to it. Already over a little time you will have found viewing getting easier I am sure. Anyway, good luck and enjoy the views.

Thanks James and Robin for your very valued input!

I think as you say it is a case of getting to know whats what, I have found things much easier since I first got the telescope.

I'm taking it very much as a marathon rather than a sprint, the heavens will still be there next month, next year and next millenium so whats the hurry? So I am learning, slowly but surely.

I really appreciate everyone's help, its nice on here that the more experienced people are more than willing to help newbies even though they must have heard the sames questions many times over!

Rose

[rwilkey]

Hi Rose, we have all been there, and are with you all the way!