Barlow problem

[Abhishek]

Hi 

I have the  telescope powerseeker 80az celestron but I'm not able to view any planets using the Barlow they have given me. It's a 3x, I have been given a 25mm lens and a 4mm lens. Kindly help me out. 

[DaveL59]

Does the 4mm work ok not barlow'd on the planets? 

That barlow would only be useful with the 25mm eyepiece giving you an effective 8mm. The 4mm eyepiece would put the magnification way over what that scope would be able to handle and you'd just see blackness. It should work with the 25mm though and give a higher magnification compared to the 25mm alone. You would need to be very centred on the target as shifting the magnification that far would put you off target otherwise and then you'd need to hunt for it again.

[Abhishek]

Hi dave 

The 4mm eyepiece is really small I can hardly see things clearly with it. I tried to put the Barlow and then the 25mm eye piece today I really couldn't see anything clearly 

[Robindonne]

I also have a barlow that doesn’t work.  At least not on all setups.  Some do some dont.  That’s  to keep this hobby a bit exiting 

Edited July 29, 2020 by Robindonne

[DaveL59]

1 hour ago, Abhishek said:

Hi dave 

The 4mm eyepiece is really small I can hardly see things clearly with it. I tried to put the Barlow and then the 25mm eye piece today I really couldn't see anything clearly 

sadly the eyepieces that are supplied with many scopes aren't always the best. The 25mm should be usable but the 4mm is that an SR4 by any chance or a plossl? The smaller the focal length (mm) the smaller the eye lens tends to be so it can be hard to use. If they supplied an SR4 then it's pretty much no use. Barlows can vary in quality too and a 3x isn't as useful as a 2x I think, at least in my experience.

I'm guessing your mount isn't a tracking or goto type, so by the time you switch from the 25mm to that plus barlow the object you aimed at will have drifted across the field of view and would need to be found again. So you really need to get it well centred and perhaps even over to the left a little, so that if you are quick it might have stayed in view after swapping over. Have a try at the moon and see how switching over goes so you get an idea of the change in magnification and also how the target shifts. Also being very bright the 4mm might give you a view you can use.

If you do decide you want to do more, then upgrading the eyepieces and barlow may be a good idea but ask here for advice and recommendations and focal lengths. We'll need the details of the scope - 80mm F400 is it? Assuming it is the 80AZS, looking that up it's supplied with an erect image diagonal, 20mm and 4mm plossl and a long 3x barlow. So that would give you magnifications:

25mm  x16
20mm  x20
4mm   x100

Max useful magnification they state is x189 so the barlow is of no use with the 4mm as that significantly exceeds the scope's abilities. With the barlow and 25 or 20mm it would yield x48/x60 depending which you have. Planets will still look very small so you'd need the 4mm on its own to get a slightly better view.

[Mr niall]

Can you see distant things ok in the daytime? Try it out on something as far away as you can in the daylight.

Can you give us more specific information on what the problem is? 

Is it that it doesn't reach focus, or gets near focus - or you aren't sure if anything happens or what focus should look like? Or that you are struggling to achieve fine focus, or that you are getting close to focus but not quite there? Are things fuzzy? Or just not there?

Are you experiencing the exact same thing with the different eyepieces or a different thing with each eyepiece?

With the 4mm you'll need to get really close to the eyepiece so would be difficult with spectacles for example.

With that scope the 20mm eyepiece will be your main eyepiece for most stuff. The 4mm is useful for moon and planets only.

The barlow is "kind of" usable for daytime use but I wouldn't bother with it at all for night time use personally. Celestron have a habit of adding strange accessories to ensure they can advertise a scope as achieving 10,000x or whatever but that kind of misses the point. You shouldn't really bother with the barlow at night. It wont add anything to the experience. 99% of observing is done in the 20-75x magnification range anyway. Have you got the F4 version (400mm?) - if so the 4mm eyepiece will give you 100x magnification which is a reasonable max for that scope. The barlow shouldnt figure anywhere in that equation.

Edited July 29, 2020 by Mr niall

[Abhishek]

13 hours ago, DaveL59 said:

sadly the eyepieces that are supplied with many scopes aren't always the best. The 25mm should be usable but the 4mm is that an SR4 by any chance or a plossl? The smaller the focal length (mm) the smaller the eye lens tends to be so it can be hard to use. If they supplied an SR4 then it's pretty much no use. Barlows can vary in quality too and a 3x isn't as useful as a 2x I think, at least in my experience.

I'm guessing your mount isn't a tracking or goto type, so by the time you switch from the 25mm to that plus barlow the object you aimed at will have drifted across the field of view and would need to be found again. So you really need to get it well centred and perhaps even over to the left a little, so that if you are quick it might have stayed in view after swapping over. Have a try at the moon and see how switching over goes so you get an idea of the change in magnification and also how the target shifts. Also being very bright the 4mm might give you a view you can use.

If you do decide you want to do more, then upgrading the eyepieces and barlow may be a good idea but ask here for advice and recommendations and focal lengths. We'll need the details of the scope - 80mm F400 is it? Assuming it is the 80AZS, looking that up it's supplied with an erect image diagonal, 20mm and 4mm plossl and a long 3x barlow. So that would give you magnifications:

25mm  x16
20mm  x20
4mm   x100

Max useful magnification they state is x189 so the barlow is of no use with the 4mm as that significantly exceeds the scope's abilities. With the barlow and 25 or 20mm it would yield x48/x60 depending which you have. Planets will still look very small so you'd need the 4mm on its own to get a slightly better view.

Hi dave could I email you the photos of my lenses so you could tell me if they are of any use or nah?Would also like to correct myself. The lens is a 20mm eye piece and the Barlow is 3x. I tried to see the planet using the Barlow and then attaching the 20mm. I could not see anything. The 4mm is really small to view it from which makes it harder for me to see anything to be honest. My telescope is a celestron powerseeker 80az. Yes it has  a 400mm focal length 

[Abhishek]

13 hours ago, Mr niall said:

Can you see distant things ok in the daytime? Try it out on something as far away as you can in the daylight.

Can you give us more specific information on what the problem is? 

Is it that it doesn't reach focus, or gets near focus - or you aren't sure if anything happens or what focus should look like? Or that you are struggling to achieve fine focus, or that you are getting close to focus but not quite there? Are things fuzzy? Or just not there?

Are you experiencing the exact same thing with the different eyepieces or a different thing with each eyepiece?

With the 4mm you'll need to get really close to the eyepiece so would be difficult with spectacles for example.

With that scope the 20mm eyepiece will be your main eyepiece for most stuff. The 4mm is useful for moon and planets only.

The barlow is "kind of" usable for daytime use but I wouldn't bother with it at all for night time use personally. Celestron have a habit of adding strange accessories to ensure they can advertise a scope as achieving 10,000x or whatever but that kind of misses the point. You shouldn't really bother with the barlow at night. It wont add anything to the experience. 99% of observing is done in the 20-75x magnification range anyway. Have you got the F4 version (400mm?) - if so the 4mm eyepiece will give you 100x magnification which is a reasonable max for that scope. The barlow shouldnt figure anywhere in that equation.

Hi 

I will avoid using the Barlow in the night but with my 4mm, it is really difficult to see anything because of how small it really is and it's only the 20mm that helps me view the moon but yesterday when I tried to view the planets it gave me a really hard time. I could not see anything until I zoomed in it really didn't help me much. The 20mm has been the only useful lens. Could you help me out? Can I send you the images of my lenses if that can help you understand my difficulty? 

[DaveL59]

be best to post pictures here in the thread as others will be able to add too. I expect they are basic plossl eyepieces and there are a lot better ones out there but it is what you have to work with. It is a beginner scope so will have limitations for sure, the eyepieces, the diagonal both could be improved upon. For astro you would be better to get/use a 90-degree star diagonal than an erecting one, you get an inverted image but less light loss. As mentioned by Niall, the supplied barlow will not be very useful, better to get another eyepiece in the 8-12mm range perhaps. Depends on how much more you're prepared to spend tho as eyepieces like the BST Starguiders are around £50 each for example. These can then be used on other scopes as you upgrade but it's an investment right after getting a scope that may not be what you want to do right now.

[Mr niall]

26 minutes ago, Abhishek said:

Hi 

I will avoid using the Barlow in the night but with my 4mm, it is really difficult to see anything because of how small it really is and it's only the 20mm that helps me view the moon but yesterday when I tried to view the planets it gave me a really hard time. I could not see anything until I zoomed in it really didn't help me much. The 20mm has been the only useful lens. Could you help me out? Can I send you the images of my lenses if that can help you understand my difficulty? 

No its ok I know what lenses look like. Telescopes are all much of a muchness, if you can expand on the questions I asked above it should help. We cant help unless you can expand on what statements like "gave me a really hard time" mean. Hard time how? Specifically?

But, when you say "zoomed in"....

Forgive me if I'm way off here but...

You are aware that magnification is a fixed product of the relationship between the focal length of the scope and the focal length of the eyepiece? So if you have a focal length of 400mm (length of the scope) then a 20mm eyepiece would give you a magnification of 20x - 400/20 = 20. Similarly a 4mm eyepiece would give you a magnification of 100x (400/4 = 100).

Every eyepiece is a slightly different construction and design. Just to be clear - you are aware that the little wheel on the side of the scope is for focussing right? Not for zooming in like a camera lens? That knob is to bring the eyepiece into focus only, it doesn't zoom anything.

Each eyepiece gives you one magnification only.

Edited July 30, 2020 by Mr niall

[Abhishek]

39 minutes ago, DaveL59 said:

be best to post pictures here in the thread as others will be able to add too. I expect they are basic plossl eyepieces and there are a lot better ones out there but it is what you have to work with. It is a beginner scope so will have limitations for sure, the eyepieces, the diagonal both could be improved upon. For astro you would be better to get/use a 90-degree star diagonal than an erecting one, you get an inverted image but less light loss. As mentioned by Niall, the supplied barlow will not be very useful, better to get another eyepiece in the 8-12mm range perhaps. Depends on how much more you're prepared to spend tho as eyepieces like the BST Starguiders are around £50 each for example. These can then be used on other scopes as you upgrade but it's an investment right after getting a scope that may not be what you want to do right now.

Sounds good. I'm attaching the image of my 4mm lens and Barlow. 

[Abhishek]

21 minutes ago, Mr niall said:

No its ok I know what lenses look like. Telescopes are all much of a muchness, if you can expand on the questions I asked above it should help. We cant help unless you can expand on what statements like "gave me a really hard time" mean. Hard time how? Specifically?

But, when you say "zoomed in"....

Forgive me if I'm way off here but...

You are aware that magnification is a fixed product of the relationship between the focal length of the scope and the focal length of the eyepiece? So if you have a focal length of 400mm (length of the scope) then a 20mm eyepiece would give you a magnification of 20x - 400/20 = 20. Similarly a 4mm eyepiece would give you a magnification of 100x (400/4 = 100).

Every eyepiece is a slightly different construction and design. Just to be clear - you are aware that the little wheel on the side of the scope is for focussing right? Not for zooming in like a camera lens? That knob is to bring the eyepiece into focus only, it doesn't zoom anything.

Each eyepiece gives you one magnification only.

My bad, I used the wrong term. I meant focus at thr first place. By hard time I meant that the construction of the 4mm is so small that I'm not really able to see anything through it. I have attached an image on the reply where dave replied. Please let me know if you can see it. What I really meant to say is that my 4mm lens has been really not helpful. It's only the 20mm for the moon and not the planets since I can't really see much through it. With the 4mm, maybe it's the construction of the lens that's making it hard for me to see anything through it. I adjust the focus with the knob but it doesn't really help. I would really like to know what should be my next step in seeing planets. That will be really appreciated 

[Mr niall]

Just now, Abhishek said:

My bad, I used the wrong term. I meant focus at thr first place. By hard time I meant that the construction of the 4mm is so small that I'm not really able to see anything through it. I have attached an image on the reply where dave replied. Please let me know if you can see it. What I really meant to say is that my 4mm lens has been really not helpful. It's only the 20mm for the moon and not the planets since I can't really see much through it. With the 4mm, maybe it's the construction of the lens that's making it hard for me to see anything through it. I adjust the focus with the knob but it doesn't really help. I would really like to know what should be my next step in seeing planets. That will be really appreciated 

I understand.

Well that isnt a plossl, its a Kellner or MA derivative but the point actually applies to Plossls too so its a moot point. Its a fairly standard issue 4mm eyepiece and not that amazing.

You have a short focal length scope. Which means getting high magnifications will be a challenge. Short focal length achromatic refractors suffer from chromatic aberration at high magnifications. This causes a violet or purple halo that can be quite a sight. That shouldnt put you off - I'm just letting you know its perfectly normal.

With your scope - really, I'd probably aim for no higher than 80 or 90x. The good news is you can see the cloud bands on jupiter at 25x and get a good view of Saturn at 50x so that is good.

Eyepieces - well. The biggest problem with eyepieces of that type of anything 10mm or higher is their "exit pupil" and "field of view". Exit pupil is the maximum distance your eye can be away from the eyepiece and still be able to see the whole field of view. In your 4mm it is probably about 3.5 to 4mm which is why you are struggling. You need an eyepiece with a much bigger exit pupil. And that is also why your 20mm eyepiece is easier to use as it has a much bigger exit pupil.

You have two choices:

1. Buy a new eyepiece. As @DaveL59, the BST Starguider is a good choice.  But expensive. Another cheaper choice is the 66 degree 6mm super wide angle eyepiece. They are a clone and sold under a thousand different brands but you can find them for about £25 from the far east if you check the usual suspects.

2. Actually use your barlow. One of the quirks of Barlows is that they actually preserve the exit pupil. So if you use your 20mm eyepiece with your barlow then you effectively have a 6.7mm eyepiece with the same exit pupil as your original 20mm eyepiece. Maybe try having a play around with that.

The other things to take into account are field of view and focussing. Focussing at higher magnifications is trickier as you have to be more delicate to get it right. Additionally the amount of sky that that scope sees at higher magnifications is much narrower so you have to be a tad more precise. And to top it off, any "wobble" when you touch your scope is massively exacerbated by high magnifications. So keeping stuff in the field of view and focussing takes a bit of practice.

Best of luck!

[Abhishek]

1 hour ago, Mr niall said:

I understand.

Well that isnt a plossl, its a Kellner or MA derivative but the point actually applies to Plossls too so its a moot point. Its a fairly standard issue 4mm eyepiece and not that amazing.

You have a short focal length scope. Which means getting high magnifications will be a challenge. Short focal length achromatic refractors suffer from chromatic aberration at high magnifications. This causes a violet or purple halo that can be quite a sight. That shouldnt put you off - I'm just letting you know its perfectly normal.

With your scope - really, I'd probably aim for no higher than 80 or 90x. The good news is you can see the cloud bands on jupiter at 25x and get a good view of Saturn at 50x so that is good.

Eyepieces - well. The biggest problem with eyepieces of that type of anything 10mm or higher is their "exit pupil" and "field of view". Exit pupil is the maximum distance your eye can be away from the eyepiece and still be able to see the whole field of view. In your 4mm it is probably about 3.5 to 4mm which is why you are struggling. You need an eyepiece with a much bigger exit pupil. And that is also why your 20mm eyepiece is easier to use as it has a much bigger exit pupil.

You have two choices:

1. Buy a new eyepiece. As @DaveL59, the BST Starguider is a good choice.  But expensive. Another cheaper choice is the 66 degree 6mm super wide angle eyepiece. They are a clone and sold under a thousand different brands but you can find them for about £25 from the far east if you check the usual suspects.

2. Actually use your barlow. One of the quirks of Barlows is that they actually preserve the exit pupil. So if you use your 20mm eyepiece with your barlow then you effectively have a 6.7mm eyepiece with the same exit pupil as your original 20mm eyepiece. Maybe try having a play around with that.

The other things to take into account are field of view and focussing. Focussing at higher magnifications is trickier as you have to be more delicate to get it right. Additionally the amount of sky that that scope sees at higher magnifications is much narrower so you have to be a tad more precise. And to top it off, any "wobble" when you touch your scope is massively exacerbated by high magnifications. So keeping stuff in the field of view and focussing takes a bit of practice.

Best of luck!

I did try using the Barlow with the 20mm but I wasn't able to see much. Maybe as you said it's hard to see at night that's why. I'll try these again tonight and I'll get back to you soon on it. Thanks this really helps! 

[AstroMuni]

5 hours ago, Mr niall said:

One of the quirks of Barlows is that they actually preserve the exit pupil.

I dont think thats quite true. But happy to be corrected 🙂

The exit pupil can be calculated as Focal length of eyepiece/ Focal ratio of scope. So assuming it was an F5 scope in first instance that would have given the 20mm an exit pupil of 4mm (20/5). But adding the 3x Barlow would effectively make it a F15 scope and the exit pupil would be 20/15=1.3mm

Edited July 30, 2020 by AstroMuni

[AstroMuni]

3 hours ago, Abhishek said:

I did try using the Barlow with the 20mm but I wasn't able to see much.

Having read your posts I am trying to figure out what your problem is. Feel free to correct me.

Where are you trying to view from? Inside your house, through a window or out in the clear? How bad is the light pollution in your area (i.e. are you in the middle of a busy city)

Using the Barlow + 20mm:

1. Have you tried this in daytime to view a distant object?

2. Are you able to achieve focus when viewing the moon?

 

 

[Mr niall]

50 minutes ago, AstroMuni said:

I dont think thats quite true.

The exit pupil can be calculated as Focal length of eyepiece/ Focal ratio of scope. So assuming it was an F5 scope in first instance that would have given the 20mm an exit pupil of 4mm (20/5). But adding the 3x Barlow would effectively make it a F15 scope and the exit pupil would be 20/15=1.3mm

Yep you are correct - good spot. I meant eye relief not exit pupil. 

[Abhishek]

2 hours ago, AstroMuni said:

Having read your posts I am trying to figure out what your problem is. Feel free to correct me.

Where are you trying to view from? Inside your house, through a window or out in the clear? How bad is the light pollution in your area (i.e. are you in the middle of a busy city)

Using the Barlow + 20mm:

1. Have you tried this in daytime to view a distant object?

2. Are you able to achieve focus when viewing the moon?

 

 

Hi 

I'm trying ng to view it from my terrace. I'm in the middle of a steel city so you can probably imagine the pollution. 

I havent tried using the Barlow in daytime as yet. 

I tried viewing the moon today using the Barlow +20mm. Wasn't able to achieve the focus as I had expected. It wasn't really clear to be frank. Maybe it was the sky but I tried rotating the knob here and about but didn't achieve the focus. 

[DaveL59]

worth trying it without the diagonal in the path, perhaps, in case that is adding too much extra length to the light path, are you getting closer to focus as you rack inward but just not quite getting there? 

I'd suggest remove the diagonal and just slot the barlow and eyepiece directly in the scope focuser tube. If that lets you reach focus then you'd maybe need to get a regular star diagonal as that'll add less compared to the erecting diagonal. Would also affirm that the barlow supplied is really for terrestrial use and not astro and perhaps getting a 2x shorter barlow as well would then gain you the flexibility, at least with the 20mm.

[Abhishek]

Hi guys 

For everyone who replied, thank you very much. Everything worked perfectly. I was able to see Saturn and jupiter. They looked amazing. I had to use the 4mm without the 3x Barlow. 

I was also able to see the irregular surface  pattern of jupiter which really looked like an amoeba 

[Pixies]

2 hours ago, Abhishek said:

Hi guys 

For everyone who replied, thank you very much. Everything worked perfectly. I was able to see Saturn and jupiter. They looked amazing. I had to use the 4mm without the 3x Barlow. 

I was also able to see the irregular surface  pattern of jupiter which really looked like an amoeba 

So often, advice is given but the original poster is never seen again. It's great that you came back to let us know how it's going. It also shows that you are going to be sticking around - lots to learn here and a lot to give too.

Clear skies!

[Ricochet]

On 06/09/2020 at 18:23, Abhishek said:

Hi guys 

For everyone who replied, thank you very much. Everything worked perfectly. I was able to see Saturn and jupiter. They looked amazing. I had to use the 4mm without the 3x Barlow. 

I was also able to see the irregular surface  pattern of jupiter which really looked like an amoeba 

If Jupiter looked like an amoeba then I think it is likely you are not in focus. To focus you must turn the focuser to make the object as small as possible. Jupiter should appear as a small disk with a couple of stripes across it and up to four moons orbiting around it, each one looking like a small point of light.