I can duplicate your exact problem. I and many others have complained about this BUG since probably Version 1 of Lightroom. Unfortunately, Adobe considers this a FEATURE instead of a BUG. I am sure they could fix the problem but will not. I also think this is a serious failing and an absolutely poor design choice, both in the original design and their refusal to fix/change it. I don't know what their tolerance is in this supposed feature but this example is off by 0.5%. I think you are going to have to live with the problem because Adobe will probably not change it as they seem real proud of this feature/bug.
John Ellis created a LR plugin that allows custom crops like 2600x2000 and more: Any Crop Lightroom Plugin
Adobe designers DO NOT consider this a bug. This was correctly reported as a bug 2 years ago by Rikk Flohr of Adobe but the reply 5 months ago by Simon Chen of Adobe that they have a .005 threshold shows the programmers think this should be considered a FEATURE. Extremely poor design decision. I am sure it is not going to get changed/fixed.
Adobe designers DO NOT consider this a bug. This was correctly reported as a bug 2 years ago by Rikk Flohr of Adobe but the reply 5 months ago by Simon Chen of Adobe that they have a .005 threshold shows the programmers think this should be considered a FEATURE.
In a follow-up to Simon, I showed how to properly compare aspect ratios and fix this problem: Lightroom: I can't add (certain) custom crop ratios | Photoshop Family Customer Community. My Any Crop plugin proves my analysis correct.
It should be a one-line fix, replacing the expression:
abs (round (crop.h) / round (crop.w) - preset.h / preset.w) <= 5e-3
abs (crop.h / crop.w - preset.h / preset.w) <= 7.7e-6
If more people me-too vote on the topic in the feedback forum, and more importantly, provide a polite but detailed opinion of why they want the issue addressed, and include a link to my analysis of the fix, it may get their attention. It seems that in the past few weeks, there's been more attention paid to the feedback forum. (But I suggest avoiding the semantic rathole of "bug versus feature" -- the important point is that LR's current behavior isn't meeting customers' needs, and there is an easy fix.)
Thanks for the added info on this issue. I have been discussing this issue in several threads for years and all the comments I have seen from Adobe is that it was an as-designed feature and no changes would be considered. For my own use the present behavior has not caused me any problems but I think it should be more accurate than the present .5 percent. Your numbers look great and I thought it should be a simple change of the tolerance in the code. Its great to see that Simon Chen and the others at Adobe are looking at these kind of behaviors in Lr. Jeffery Tranberry seem to be leading the development/improvement of Lightroom in the right direction by focusing a little more on bug fixes and usability tweeks. I will add a note to the thread you linked above and avoid any "complaining"
I can't understand why this "feature" would be an advantage to any user? If Photoshop rounded the file sizes that users created by some arbitrary amount such as 0.005% users would be rightly appalled. If I want to output my image at 2600 x 2000px why does Lightroom prevent me?
It's a lot of extra work for me to fix this, as I sometimes need to create hundreds of images at this size which my client has specified.
I'm going to try out John Rellis's plug-in to see if that helps, but I still don't understand why Adobe don't fix this problem.
I still don't understand why Adobe don't fix this problem.
We can only make educated guesses as to why they don't fix the problem. Overall, in the past many years Adobe has not made fixing bugs a high priority. But recently, in response to a popular "open letter" in the official feedback forum, Chief Customer Advocate Jeffrey Tranberry responded:
Hi folks, I wanted to reply and say we're following this discussion and are sympathetic to your concerns. We've been having recent, ongoing discussions within our product teams about how to best pace releases - balancing feature work, bug fixing, polish and architectural improvements.
Based on Adobe's responses in the forum recently, it looks like they are making an effort to change how they respond to problem reports.
This particular issue was examined five months ago by Simon Chen, Adobe Principal Computer Scientist, who determined that it was an unavoidable consequence of the way computers do numerical computations. That was not an unreasonable surmise, and it's probably that his analysis caused the issue to be changed from a bug report to a "feature request" and perhaps to get de-prioritized.
But his analysis was incorrect, as I've demonstrated. I'm guessing that no one at Adobe has seriously revisited the issue since then. To his credit, Simon is an active, constructive participant in the forums, but I'm sure he has tons of email and is trying to focus on the issues where he thinks he can be most effective.
The best way to influence Adobe is to me-too vote on the topic and provide a detailed opinion about the issue. Adding an opinion will cause the issue to appear at the top of the feed for anyone reading that forum, and it will send additional emails to employees Rikk Flohr and Simon Chen. (Note that this forum is a user-to-user forum in which product developers rarely participate.)
Also, while I enjoy developing plugins, I would much prefer that each plugin's' functionality were incorporated into LR. (The LR plugin market is too small for any developer to make much money.)
John, I discovered a similar issue about a year ago in the Print module as described here: Re: Print module export to JPEG quality loss?
There's a rounding error that causes a stretching of the long edge, which crops off a few pixels. This interpolation error also softens the JPEG output file. It may also be happening in the printer data output, but I haven't tested it. LR 6.7 exhibits the same behavior. I filed a bug report here: Lightroom: Print Module crops image when using custom file dimensions | Photoshop Family Customer Community
Adobe hasn't 'Acknowledged' this as a problem to date. IMHO these are small, easily fixable bugs that would be caught if adequate testing was performed on each new update by a separate Quality Control team. There have been similar issue with PS and other Adobe apps so it appears to be corporate-wide and not just with LR.....very disappointing. I've added my vote to your Bug Report/Idea.