Sorry CHG_CANON, your posts are usually pretty good, but this time you had a swing and a miss.
The OP was asking why anyone would have BOTH a D500 and a D850, not one or the other.
In this case there is no significant difference in pixel density, nor is there better weather sealing in the D500. The D500 does have a slightly faster frame rate but obviously there is no cost saving in buying TWO cameras.

The only reasons I can think of for having both the D500 and the D850 are the slightly faster frame rate of the D500 and the lighter weight of a cropped sensor kit. I happen to have both a D7100 and a D850, but the D7100 is just a leftover from before I upgraded to full frame. I occasionally use the D7100 when I'm backpacking or going to be in a situation where the camera is at risk, but that's about it.

A faster frame rate for the D850 can be achieved with a battery grip much more cheaply that by buying a whole second camera, so that pretty much leaves the lighter weight as the only reason to have a D500 along with a D850. That is a pretty costly investment for very little gain in my opinion. But hey, if someone has money to waste, more power to them.

It's not just for video, but for star trails your card is plenty fast enough. No need to waste money on a faster card. A faster card may save you one second on the gaps but since you will probably be using gap filling software anyway it's totally irrelevant.

If your intervalometer allows longer exposures than 30 seconds you can always increase the exposure time and hence reduce the relative length of the gaps. Depending on the effect you are after, you may also consider cranking up the ISO. That will give you a lot more stars and many of the gaps will be filled in simply with dimmer stars.

Good luck - I hope you will post the results of your most recent efforts.

Tim

Everything seems to be working just fine. A faster card would allow you to shorten the gaps slightly but it’s probably not worth the expense just for this application. First try a gap filling program and see how you like it. It can be done in Photoshop but it’s probably more trouble than it’s worth. I’m pretty sure Starstax can do this and it’s free.

I’m not familiar with Canon cameras but I can’t believe there is really a 30 minute limit, especially if you are using an external intervalometer. I would investigate that a little further.

Tim

Sorry - I'm travelling and don't have access to my normal computer so I can't see too much in the image you posted, but what I can see looks fine. Could you please post a crop that just shows a small area and demonstrates the problem. I'm not sure what you mean by dashes and not lines. You will always get a small break in the trail during the few seconds that the buffer is dumping but that is all I can see in your image. If that is what you are concerned about there is software that can fill those in. However, I sense that this is not your concern.

Tim

Why do you think the problem wasn't fixed? Your latest image looks fine to me (for some reason I only see one). With a 5 minute equivalent exposure I think everything is as expected. The very minor breaks are due to the 4 second interval between exposures. Other than that I don't see a problem. Am I missing something?

Tim

You're welcome. Glad I could help.

Since you mentioned getting up to check on the moon, let me suggest two applications that you might not be aware of, The Photographer's Ephemeris and Photopills. Both are excellent for planning night shots. The web based version of TPE is free, the mobile version is a few dollars. Photopills is $9.99 and has a ton of useful features, including excellent videos.

Good luck on you next shoot.

I think you mean "you're".
The quality of posts is far more important than the quantity. I think you are proof of that.

Thank you insignificant amoeba.

Actually, there is no need to wait. You can run a test case anytime to verify the problem. I suggest leaving a few seconds (three?) between exposures to allow the buffer to flush. Once you have the mechanics figured out you can try again with the actual situation you are interested in.

Yes - especially you.

The other replies (save one) had nothing relevant to say regarding the question the OP asked.

You have at least two different things happening here. First, there is a misalignment of one or more images. This can be seen in the offset at the tree level. This can be easily fixed in Photoshop. When you stack, make sure you first align images. If this doesn't fix the problem, identify which image is misaligned (by turning on and off individual layers) and either align it by hand or delete it.

Second, there is the gap between star trails. The gap is a bit puzzling as it does not appear to be uniform in duration. However, it appears to be at least 30 seconds. The first thing to do is to check the metadata. Is the gap actually consistent, and if so, what is the length? The most obvious cause would be that you had long exposure noise reduction turned on. The second most obvious cause would be that you had your intervalometer set improperly. Hmmm, now that I think back on your original post, I'd elevate this to the most probable. By setting a zero delay between exposures you probably caused the problem. Your camera needs some time to flush the buffer after each exposure. If you set a zero delay, the succeeding image wants to start while the buffer is being downloaded. It can't, and so the camera has to wait for the next interval before it can start a new exposure.

You can safely ignore the other posts concerning write speed of the card, the length of your exposures, different stacking software, etc. They are irrelevant to your problem.

Those are airplanes.

My suggestion is to stick with your D7200. It is capable of producing very high quality images.

I upgraded from a D7100 to a D850 and I'm glad I did. The image quality is way better. However, obtaining that improved image quality requires high end glass. The 28-300 (which I have and use as my 'walking around lens') just won't cut it. That means bigger, heavier, and more expensive lenses. If the tiny difference in weight between the D600 and D850 is an issue for you, I can't imagine you will actually be willing to cart around any full frame camera with high end glass. In fact, maybe you should think about going the other direction and getting something like a micro 4/3 system. There you will find a noticeable weight and size savings and the image quality should still be excellent.

I agree, it is certainly possible to get good results, it's just very disappointing to me that Nikon managed to screw up such a simple feature. In the processing section of your video I noted at least one frame with a totally black mask - meaning that there were more frames than needed.

I've experimented with this feature on landscapes (Hmmm, I wonder what step size I'll need...) and macros (Well, let's see, I know the step size I just used for that landscape, now what size should it be for this flower?). Sure, trial and error can provide a guide, but why all the headache? I still find that I get to the computer with either way too many shots, shots that extend too far in focus, not far enough in focus, or steps that were slightly too large and leave areas in less than ideal sharpness.

I was a bit hasty in my initial suggestion for how to implement this function intelligently. Let me correct that on the unlikely chance that anyone is still following this. Specify the start and end focus points and the number of exposures. Done.

I think I'm a little sensitive about this as I keep hearing all these rave reviews about this camera and yet I have a list of things I don't like about it that I don't hear anyone mentioning. I'm still pretty happy with this model, but there are a lot of areas that I think could be improved.

Personally, I think the focus shift feature in the D850 is crap. Very disappointing. Why? Because there is no obvious relationship between the number of exposures and the step size. Good luck guessing the proper step size and number of exposures as you transition from macro to landscape. Odds are, you'll either come back with too few frames or too many. Manual focus shift is pretty trivial and you can tell exactly what you are getting with every exposure. Automatic focus shifting is always a guess. Why bother?

If Nikon really wanted to include this feature I think it would have been far more useful to simply have the camera focus from a starting location to infinity in a user specified number of equally spaced steps.
(i.e. cut out the step size input) That way the user is guaranteed to at least cover the full focus range with an easily estimated number of exposures.

If I am missing something regarding how to accurately determine the number of exposures and step size with the 850 I'd love to hear it and would happily revise my opinion. Until then, I'll stick with manual focusing for stacks.