28 replies to this topic

[todnik]

I have a 25mm and a 10mm for my home built dob. I am wanting to get another eye piece. I was thinking of a 6mm or 7mm or around that. would  getting a 6 or 7mm be better than a zoom eye piece?

 

Also considering this or other ideas. I don't know anything about eye pieces

 

Astromania 1.25" 6mm Plossl Telescope Eyepiece - 4-Element Plossl Design - Amazon $16

 

Alstar 1.25 inch Telescope Zoom Eyepiece - 7 to 21mm Zoom Lens Telescope Eyepiece on Amazon for $48

 

Thanks!

[vtornado]

6mm plossl will have very tight eye relief if that would be important to you.  It is 50 degrees apparent field of view (AFOV).   I would avoid it.

 

The svbony 7-21 zoom with 6 elements is very good.  It has about 60 degrees at the 7mm setting.  Eye relief is much better too.

 

You could also get a 2x barlow.

[todnik]

6mm plossl will have very tight eye relief if that would be important to you.  It is 50 degrees apparent field of view (AFOV).   I would avoid it.

 

The svbony 7-21 zoom with 6 elements is very good.  It has about 60 degrees at the 7mm setting.  Eye relief is much better too.

 

You could also get a 2x barlow.

Not sure what very tight eye relief mean.

 

Ok. So would a 2x barlow be instead of the 7- 21 zoom? and just add that to my current setup. Or get the svbony 7-21 zoom with the 2x barlow?

[RLK1]

Not sure what very tight eye relief mean.

 

Ok. So would a 2x barlow be instead of the 7- 21 zoom? and just add that to my current setup. Or get the svbony 7-21 zoom with the 2x barlow?

"Not sure what very tight eye relief mean."

 

It means your eye will be pressed up against the eyepiece to see the field of view and if you wear glasses, you may not be able to see much of it at all.

[todnik]

"Not sure what very tight eye relief mean."

 

It means your eye will be pressed up against the eyepiece to see the field of view and if you wear glasses, you may not be able to see much of it at all.

Ok. I don't wear glasses except to read. However, having my eye press against the eye piece wouldn't be a preferred and I would like to avoid. Thanks!

[SeattleScott]

The SVBONY zoom is a hard value proposition to beat starting out. Certainly it isn’t wide AFOV or long ER, so if you get the stargazing bug, you will likely upgrade to better eyepieces. But it would get you going and allow you to gauge interest for the price of a nice restaurant dinner.

[sevenofnine]

+1 on the SVB 7-21mm 6 element zoom lens. Good luck with your choice! 

 

https://www.amazon.c...rd_i=B07Z64NK65.

[todnik]

+1 on the SVB 7-21mm 6 element zoom lens. Good luck with your choice! 

 

https://www.amazon.c...rd_i=B07Z64NK65.

Thats the one I was looking at getting. its added to my shopping list.

Edited by todnik, 13 March 2025 - 03:25 PM.

[areyoukiddingme]

Another vote for the zoom. It has ok field of view, but not great.

 

But it is relatively inexpensive and will show you want kinds of magnifications work with your scope and conditions.

[areyoukiddingme]

At 7-21mm, it's possible that the zoom will need a barlow too. They can be had relatively inexpensively. I suggest something in the 1.25" format.

 

For example, https://astronomics....-1-25-eyepieces

[todnik]

At 7-21mm, it's possible that the zoom will need a barlow too. They can be had relatively inexpensively. I suggest something in the 1.25" format.

 

For example, https://astronomics....-1-25-eyepieces

Ok. So what does the barlow do? Is it just a magnifier? like a 2x converter on a camera?

[Inkie]

Yes, a Barlow can multiply the focal length by one of several values currently on the market, and at various qualities and prices.  Some prefer only 1.5 times mag/focal length multiplying, some 2.0, some 3.0...  The Barlows, as opposed to 'focal extenders' also multiply the eye relief (how far from the field lens your eye needs to be in order to see most/all of the field of view).  Rather than pay for a $300 quality 6 mm eyepiece, an $80 Barlow will double the output of a decent 12 mm that you may have.

[havasman]

Ok. So what does the barlow do? Is it just a magnifier? like a 2x converter on a camera?

Suggest you get the zoom and give it some focuser time before you jump in on a Barlow. You may either decide you do not need one or decide you want to try a shorter focal length eyepiece for more magnification if you find you may be able to use it in your location. Something like the Astro-Tech 4mm UWA or Astro-Tech Paradigm Dual ED 5mm are likely to give you all the magnification that will often be useful.

[Jay_Reynolds_Freeman]

If you are considering a zoom eyepiece, the SvBONY 3-8 mm might be a particularly good choice.

 

My reasoning is that you probably have more need of a higher magnification than your 10 mm will provide, and not so much for magnifications in between what the 10 mm and the 25 mm will do. The 3-8 mm zoom spans the range from a bit more magnification than your 10 mm -- 150x -- to just about as much magnification as you would ever want to use on an 8-inch telescope -- 400x. *IF* the zoom eyepiece works for you -- and at f/6, some zoom eyepieces may have problems -- then it will provide plenty of choices for medium to high magnification work, which you will need, depending on seeing an on what you want to look at.

 

A 7-21 or 8-24 mm zoom does not give you the option of using powers that would be considered "high" for an 8 inch, on those occasions when you want them.

 

My comment about probably not needing magnifications between the 25 mm and the 10 mm is based on my own experience with deep-sky observing; 25 mm produces 48x and probably at least a one-degree field, which is useful for finding things, for looking at wide objects, and for looking at low surface-brightness objects. 10 mm would give you a magnification of 120, which is pretty much what I would choose for observing galaxies and many clusters. Your mileage may vary. 

 

I am not saying that an eyepiece of 15 to 18 mm focal length would not be useful, just that it would be less useful than higher magnifications.

 

Again I stress, not all zoom eyepieces will work at f/6. Try before you buy if at all possible.

 

 

Clear sky ...

[todnik]

I looked a little at the options and looked at the price of the 3-8mm and that is out of my range. My range is in the $50 to 70 at most for now. I wish I had a higher budget but I don't. I think I am going to give the 7-21mm zoom a try.

 

Thanks everyone for your input.

[todnik]

Ok. I got out my scope tonight with the new zoom Svbony 7-21mm eyepiece FMC. I decided to look at Jupiter again now that I know it is Jupiter. I have some questions on results.

 

1. It seems like the clarity is not as good as my Sbony 25mm eyepiece. Is that because I have a 25 and not a 21? Or is it because its a zoom lens? Also, does quality make a difference in how sharp the image can be? I did notice when I held just the zoom lens in my hand it rattles a little bit. Like something could be loose. Is it suppose to do that? Or is that normal for zoom lens?

 

2. Does air temp make a difference? I notice that using my 25mm I got to almost as good of clarity as I did when I used it a week ago when it was warmer out. However, the clarity was better then. Temp was only maybe about 20 degrees warmer than it was tonight. Tonight it was 39 to 41 degrees Fahrenheit. Doe this matter?

 

Any thoughts? Any feed back is welcome. Thanks!

Edited by todnik, 17 March 2025 - 10:24 PM.

[T1R2]

Its normal for zooms to rattle, they have moving parts, 171x on the 7mm setting is a Decent planetary power, but the jet stream of an influx of air moving into your area can cause the views to be poor and moving and not very steady, then you have the cooling off of the scope to worry about and collimation very very important...the 25mm being  sharper than using the zoom indicates to me that you probably need to collimate the scope, usually when a scope is misaligned lower powers look sharper than higher powers, but the atmosphere can also do this, so the longer you do this the more knowledge you gain and the better you'll get at determine what the problem may be. and its also a good idea to watch the weather to know where the jet stream is in relation to your viewing location, twinkling stars is a good indication seeing is not the best, but could get better through the night or get worse. 

[todnik]

Its normal for zooms to rattle, they have moving parts, 171x on the 7mm setting is a Decent planetary power, but the jet stream of an influx of air moving into your area can cause the views to be poor and moving and not very steady, then you have the cooling off of the scope to worry about and collimation very very important...the 25mm being  sharper than using the zoom indicates to me that you probably need to collimate the scope, usually when a scope is misaligned lower powers look sharper than higher powers, but the atmosphere can also do this, so the longer you do this the more knowledge you gain and the better you'll get at determine what the problem may be. and its also a good idea to watch the weather to know where the jet stream is in relation to your viewing location, twinkling stars is a good indication seeing is not the best, but could get better through the night or get worse. 

Ok. I was concerned that the little rattle was an issue. Good to know. Did not know Jet stream played a role. I will have to keep that in mind. Now that I think of it it was a little more breeze tonight as the scope was not 100% still. Wind of about 6 or 7 mph wind at about 40 degrees makes it 32 degrees with windchill. After about 20 to 30 minutes I was ready to call it quits because my hands was so cold the felt like they were freezing. So the mirror is affected by the temperature then? Makes sense. I did check the collimation after and it is a little off but not too bad. Just so slightly out of center.

 

So I can I blame it on the weather? Just kidding. I know I don't have enough experience. Only been using it a couple of times. But the first night I was out it was nice and warm for being early spring and no wind at all and I stayed out for about a couple hours or so. Tonight I could barely handle 40 mins.

[SeattleScott]

The views will be worse, particularly at higher magnification, until the scope cools down to the same temperature as the outside air. I always either set the scope out ahead of time to cool, or start with low power targets first.

The scope might need to be collimated, or possibly the eyepiece is contributing. Actually, let me correct that. The scope needs to be collimated, and the quality of the zoom could also be a factor. I feel like SVBONY makes 1,000 zooms so it can be hard to keep track of which ones are better or worse. And then there can be sample variation even among the good ones. And yes, typically zooms aren’t quite as good as fixed eyepieces.

[todnik]

The views will be worse, particularly at higher magnification, until the scope cools down to the same temperature as the outside air. I always either set the scope out ahead of time to cool, or start with low power targets first.

The scope might need to be collimated, or possibly the eyepiece is contributing. Actually, let me correct that. The scope needs to be collimated, and the quality of the zoom could also be a factor. I feel like SVBONY makes 1,000 zooms so it can be hard to keep track of which ones are better or worse. And then there can be sample variation even among the good ones. And yes, typically zooms aren’t quite as good as fixed eyepieces.

Ok. Thanks! That makes sense. When I first got out there I was wondering why it looked so bad. I figured it was the new zoom eye piece. So I switch to my 25mm right away and still did not look as good as it did the other time I had my scope out. I was only out side for a few minutes at that point as it only takes me about two minutes to setup my scope. So that make sense. I just left the house at 70 degrees and outside the windchill was 32. I did not think to let it cool down. However, after about 20 minutes or so it was looking better and more clear. but at this time I was struggling with my hands being too cold. I only gave it another 15 to 20 minutes and called it a night. Seems to be a lot of variables to consider when using a scope? I was more worried that the new eye piece was bad.

 

So my guess is this is a summer hobby mostly?

Edited by todnik, 18 March 2025 - 07:02 AM.

[SeattleScott]

A refractor doesn’t take as long to acclimate (in part because the aperture is usually small). Cassegrain can be wrapped in Reflectix to help with coll down. With a Dob and cold temps, I would set up, go inside for maybe 30 minutes, then come back out. Of course that depends on your neighborhood, and likelihood of the scope still being there 30 minutes later.

But yeah, warm weather is more enjoyable and we tend to stay out longer.

But then again, good luck seeing Orion Nebula in summer. The sky changes with the seasons, and there are some goodies in winter that you don’t want to miss.

And in Seattle, in winter, I might get one or two clear nights a month. So when they come, I tend to be motivated to stargaze. In the summer it’s normally clear, so it can be like I think I will watch a movie tonight and stargaze tomorrow.

[todnik]

A refractor doesn’t take as long to acclimate (in part because the aperture is usually small). Cassegrain can be wrapped in Reflectix to help with coll down. With a Dob and cold temps, I would set up, go inside for maybe 30 minutes, then come back out. Of course that depends on your neighborhood, and likelihood of the scope still being there 30 minutes later.

But yeah, warm weather is more enjoyable and we tend to stay out longer.

But then again, good luck seeing Orion Nebula in summer. The sky changes with the seasons, and there are some goodies in winter that you don’t want to miss.

And in Seattle, in winter, I might get one or two clear nights a month. So when they come, I tend to be motivated to stargaze. In the summer it’s normally clear, so it can be like I think I will watch a movie tonight and stargaze tomorrow.

My neighborhood is fairly safe. No porch or yard pirates. But why take the chance as people do drive by and look as I am close to the county road. About 50 feet or so. Maybe next time I set it up in my back yard and then give it time. Out of sight and wont have light interference from passing cars. I think that was my main issue was I set it up quick in about 2 minutes and started looking and got disappointed thinking something was wrong with the new eye piece. Then switching out to other one and then wondering what was wrong at that point. Not realizing ambient temp has a factor in image quality. 

 

So having the telescope out that long and at that temperature does not hurt the scope? I was kind of wondering about that.

 

I am looking forward to seeing lots of stuff. Now that I have the bug. I am considering doing my own mirror for my next build. But not sure how big to go? We will see how that goes....

 

Thanks!
 

Edited by todnik, 18 March 2025 - 08:18 AM.

[SeattleScott]

I have gone out stargazing in the snow before. Might not be recommended if you have some sensitive electronics for imaging, but no problem for a Dob.

Just be careful bringing it back inside. If you go straight from frozen Dob to 70 degrees, water will quickly condense on the primary mirror. So you need a way to gradually warm the scope back up. Like put it in an unheated garage for a couple hours before bringing it in. (Or just always storing it in unheated garage.) If you don’t have the luxury of an unheated garage, wrap it in something when you bring it in. I use a $100 padded telescope case. Some people use a sleeping bag. Others might just put a cap on each end, even a shower cap if nothing else. I wonder though if that really slows down the acclimation enough to avoid condensation.

Ironically, I bought my padded telescope bag for backyard stargazing, not driving to dark skies. When driving to dark skies, the car seat is the padding. And getting in a cold car that gradually warms up on the way home prevents condensation. I didn’t get the padded bag to protect the scope from kinetic forces. I got it to protect the mirror from condensation when I come inside.

So no, the cold won’t hurt the Dob. The warm 70 degrees in your house when you come back in, that’s what you have to be careful with.

[todnik]

I have gone out stargazing in the snow before. Might not be recommended if you have some sensitive electronics for imaging, but no problem for a Dob.

Just be careful bringing it back inside. If you go straight from frozen Dob to 70 degrees, water will quickly condense on the primary mirror. So you need a way to gradually warm the scope back up. Like put it in an unheated garage for a couple hours before bringing it in. (Or just always storing it in unheated garage.) If you don’t have the luxury of an unheated garage, wrap it in something when you bring it in. I use a $100 padded telescope case. Some people use a sleeping bag. Others might just put a cap on each end, even a shower cap if nothing else. I wonder though if that really slows down the acclimation enough to avoid condensation.

Ironically, I bought my padded telescope bag for backyard stargazing, not driving to dark skies. When driving to dark skies, the car seat is the padding. And getting in a cold car that gradually warms up on the way home prevents condensation. I didn’t get the padded bag to protect the scope from kinetic forces. I got it to protect the mirror from condensation when I come inside.

So no, the cold won’t hurt the Dob. The warm 70 degrees in your house when you come back in, that’s what you have to be careful with.

Ok. I did not think of that. This is my scope. The bottom end has about 2 inches from the mirror and is open. I did a 10" tube for an 8 inch mirror. Will condensation on the mirror hurt it?
 

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[dmgriff]

Nice atming

 

The Svbony Red and Gold Line wide field eyepieces (Orion Expanse clones) 66-68 degree afov (apparent field of view) work well with a 200/1200 dob. They come in 20/15/9/6mm. They are ~35usd+/-. 

 

Maybe a 15mm and a 2x barlow added to your existing 25,10mm plossls. The 2x barlow doubles the magnification of the eyepiece. Your range would be 25mm(48x), 15mm(80x), 25mm/barlow(96x), 10mm(120x), 15mm/barlow(160x), 10mm/barlow(240x).

 

The 2x barlow doubles the focal length of your telescope (1200mm to 2400mm) or halves the focal length of the eyepiece (25mm to 12.5mm) whichever is convenient to use. The actual definition is the former, I believe. The barlow will also add a little eye relief.

 

Good luck and good skies...

Edited by dmgriff, 18 March 2025 - 11:16 AM.