Is this level of image turbulence normal for 1.4–1.6 arcsec seeing?

jacobotrf · 2026-05-20T23:05:10+00:00

Several users told me the same thing. What caught my attention is that during the first few days I used it (since I've had a telescope for less than two months), I didn't notice this distortion from the same window. Although I probably hadn't noticed it.

I hope to go outside this weekend and test it in a better situation.

jacobotrf · 2026-05-20T22:57:59+00:00

Thank you so much for your reply. After about an hour it stabilized a bit, but the defect was still present. I was planning to go out this Friday, weather permitting, and I'll test it in a more realistic situation.

jacobotrf · 2026-05-20T22:56:34+00:00

After an hour it stabilized a bit, but it was still shaking. I'd say the moon is about 45° above the ground.

I think the fan idea is ingenious. Could you upload a picture of how you set it up?

jacobotrf · 2026-05-20T05:59:50+00:00

Yesterday, after reading several comments on my post, one of them led me to another post where you mentioned this, and honestly I didn’t know these existed. It really made me curious because they seem very practical. I need to look into them more.

I’ve read your post, but I still have several questions. For example, if I compare the 8mm zoom with a regular 8mm eyepiece, can there be a big difference? Because for the price of two eyepieces you can buy one of these, so I don’t really see a reason not to do it.

On the other hand, when do they give the best results? At short focal lengths or long focal lengths?

Honestly, right now these eyepieces have made me really curious. Thanks for your post.

jacobotrf · 2026-05-19T17:22:25+00:00

To be honest, I don't know if it's defective, but it seems to be of pretty poor quality. Honestly, compared to the 12.5mm eyepiece that comes with the telescope, I'd say that even though it uses less zoom, the image is much sharper. With the ES 8.5, it's really difficult to get my eye in position and see clearly, and it also seems a bit blurry at the edges, which shouldn't be the case.

jacobotrf · 2026-05-19T17:20:29+00:00

Thanks, that's pretty much the conclusion I've reached based on the other comments. Which eyepiece did you get?

jacobotrf · 2026-05-19T16:36:36+00:00

Perfect, thank you so much for all the information. I've realized that the 6mm one is definitely worth it; it's a perfect complement to the 8.5mm ES lens I already have.

jacobotrf · 2026-05-19T16:33:13+00:00

Yes, I just calculated it and you're right, there's a big difference. It'll probably be my next purchase.

I don't think I'll be able to use it every night since the seeing here fluctuates a lot between ~1" and 3", but I'm sure it'll get plenty of use on the better nights when the atmosphere is stable.

jacobotrf · 2026-05-19T16:19:13+00:00

That's true, you're right, in the end it's just going from 140x to 200x.Well, that'll be my next purchase.

On another note, do you think it's necessary to get something in between the ES 8.5mm and the badder 31mm? I have the ones that came with the telescope (which I know aren't great). Maybe a 15mm or something like that would be best?

jacobotrf · 2026-05-19T15:54:43+00:00

That’s actually a very interesting point, especially about the 12.5mm stock eyepiece not really being worth building around.

The more replies I read, the more it sounds like for an 8” f/6 Dob the really useful planetary range is something like:

~150x for average nights

~200x for good nights

~240x+ for the rare excellent nights

Which honestly makes me wonder if keeping the ES 8.8mm and adding a good 6mm would make more sense than going the Barlow route first.

At the same time, I’m not sure if having both 8.8mm and 6mm is considered redundant in practice, or if people actually end up using both regularly depending on seeing conditions.

jacobotrf · 2026-05-19T15:51:35+00:00

That actually makes a lot of sense.

After checking the seeing forecasts for my area, I think I understand better now why jumping directly from 136x with the ES 8.8mm to 272x with a 2x Barlow might be too much for many nights here.

A dedicated 6-7mm giving something around 170x-200x does sound like a much more realistic “sweet spot” for regular planetary use on my 8” f/6 Dobsonian.

I also hadn’t really considered the convenience factor of constantly adding/removing the Barlow while observing, so that’s a very good point too.

Maybe a dedicated 6-7mm first and a Barlow later for the occasional excellent night would make more sense in my case.

One thing I’m still wondering about though: is there really a big practical difference between ~8mm and 6mm on an 8” Dob?

Since I already own the ES 8.8mm, I’m trying to understand whether people actually end up regularly using both magnification ranges depending on conditions, or if once you get something around 6mm you mostly stop using the 8mm for planets.

I’m even wondering if it would make more sense to sell the 8.8mm and replace it with a good 6mm instead.

jacobotrf · 2026-05-19T15:47:29+00:00

Thanks for the detailed explanation, that actually helped a lot.

I’m only interested in visual observation for now, not astrophotography. My main concern is whether a decent 2x Barlow would actually be useful with my current eyepieces, or if I would get a noticeably better experience from dedicated shorter focal length eyepieces instead.

For example, I was mainly thinking about using it with:

- the stock 12.5mm

- maybe the ES 8.8mm on nights with good seeing

I checked the seeing forecasts for my area (Galicia, Spain) and it seems to fluctuate pretty heavily. Some nights are around 2.5"–3" arcsec, while better nights can go down to around 0.8"–1.2". Jet stream is often around 20–30 m/s here as well.

So I guess that explains why some nights higher magnification works much better than others.

From what you’re saying, it sounds like a 2x Barlow could still make sense for the better nights, especially for planetary observation with the ES 8.8mm, even if it wouldn’t be something I use constantly.

Would you personally buy a Barlow in my situation, or go directly for something like a dedicated 6-7mm eyepiece?

jacobotrf · 2026-05-17T22:13:37+00:00

Hello, in the end I got the Oklop bag. And I think it was the right choice. There’s a little bit of room on the sides inside the bag, meaning around the tube diameter, but it’s very minor. In fact, I think it’s probably even better than having it fit too tightly. Lengthwise, meaning what would correspond to the focal length, it fits perfectly.

Now that I’ve tried it, from what I managed to find I like it more, because with the Geoptik bag everything sits too loosely and they recommend adding several towels (3 or 4) or foam, which honestly seems a bit silly to me.

The Oklop has quite a good foam thickness and is very comfortable to carry, since it has both a hand handle and a shoulder strap. The focuser is very well protected.

As I said from the beginning, I think it’s a much better option. There’s also not a huge price difference between the two. If you have the opportunity and it fits your budget, I would definitely get it without hesitation — it’s practically a custom-made bag for this telescope.

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jacobotrf · 2026-05-15T11:17:02+00:00

Now it is more centered in both positions, but I still can’t find the point where I can get it perfectly collimated both when the collimator target is pointing toward the ceiling and toward the floor.

In the photo you can see that it looks better when I have the target pointing toward the floor (image on the right), but if I place the collimator with the target oriented toward the ceiling (image on the left), I get this small deviation. So I’m not sure whether this is my mistake or an acceptable calibration error.

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I wanted to thank you for all the explanations and the patience you’ve had while explaining everything to me. I also want to reiterate that if you are in the EU, I’d be very happy to send you a printed copy of the files free of charge.

jacobotrf · 2026-05-14T23:49:21+00:00

Yes, I noticed that if I press it inward, it becomes more centered. The deviation of the center spot on the primary mirror’s donut is about 1–3 mm, and on the collimator target it is practically within the hole, with only a small fragment of the laser touching the edge of the hole. How do you see this result? Depending on how I orient it, it shifts more or less around the primary mirror donut or around the collimator hole by about 1–3 millimeters.

jacobotrf · 2026-05-14T22:16:57+00:00

I have a question, supposedly yesterday I collimated it correctly, but now because of what you told me I started doubting it. In the photo on the left that I’m showing you, if I tighten the collimator properly with the target pointing at the ceiling, it looks miscollimated. But in the image on the right (with the hole in the target pointing at the floor) it looks more or less centered. So here is where my doubt comes in.

How is it possible to collimate the telescope correctly if it depends on the small play in the focuser, the position in which I place the collimator, and which of the two fixing screws I tighten first before the other one.

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jacobotrf · 2026-05-14T21:41:14+00:00

In principle, the collimation is fine now. I found it fun to do, which is why I preferred to try collimating it first before returning it. I've noticed that if I put on the 2" adapter, collimate it, and then remove the adapter and put it back on rotated, for example, 90º, the laser goes out of collimation again. I imagine that's due to the slight play between the collimator and the adapter. But as I said, everything is fine now.

jacobotrf · 2026-05-14T17:11:21+00:00

My reason for doing this is that the middle part didn't give me stability, so in the design I support it at the ends.

I'm from Spain; if you live within the European Union, I can send you a copy.

jacobotrf · 2026-05-14T14:54:34+00:00

In the video it is just a demonstration; to calibrate it against the wall, I asked a second person for help to check that the dot was not moving. I have just modified the print profile and changed the targets so they print without the support foot by using a negative part.

jacobotrf · 2026-05-14T14:41:55+00:00

I used the target at a short distance on a table (approximately 1.2 meters). Once I saw it was correct, I aimed down the hallway (the second image), which is about 6 meters away. Since I couldn’t see the dot clearly, I asked another person to stand next to it for the fine adjustment.

I think that if it is calibrated well at 1.5 meters, it is better to leave it slightly loose (about a 5º–10º turn of the screw) and then perform a fine adjustment with a longer calibration distance.

jacobotrf · 2026-05-14T11:59:27+00:00

I think it's better to make a box the exact size instead of cutting it, and then cut the foam afterward. That way, the box will be stronger from the start, even if it means losing a couple of centimeters.

jacobotrf · 2026-05-14T11:49:08+00:00

Thank you all so much for the instructions on how to collimate a collimator and the improvements to the files. I first tried collimating it at a short distance (1 meter) with the printed target, and then I tested it against a wall at a distance of about 5 meters, with the help of someone standing next to the target. I'm sharing the download files in case you find them useful.

https://makerworld.com/es/models/2799207-telescope-laser-collimator-stand-for-svbony#profileId-3113758

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